java try assignment

The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available. See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases. See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.

The try-with-resources Statement

The try -with-resources statement is a try statement that declares one or more resources. A resource is an object that must be closed after the program is finished with it. The try -with-resources statement ensures that each resource is closed at the end of the statement. Any object that implements java.lang.AutoCloseable , which includes all objects which implement java.io.Closeable , can be used as a resource.

The following example reads the first line from a file. It uses an instance of FileReader and BufferedReader to read data from the file. FileReader and BufferedReader are resources that must be closed after the program is finished with it:

In this example, the resources declared in the try -with-resources statement are a FileReader and a BufferedReader . The declaration statements of these resources appear within parentheses immediately after the try keyword. The classes FileReader and BufferedReader , in Java SE 7 and later, implement the interface java.lang.AutoCloseable . Because the FileReader and BufferedReader instances are declared in a try -with-resource statement, they will be closed regardless of whether the try statement completes normally or abruptly (as a result of the method BufferedReader.readLine throwing an IOException ).

Prior to Java SE 7, you can use a finally block to ensure that a resource is closed regardless of whether the try statement completes normally or abruptly. The following example uses a finally block instead of a try -with-resources statement:

However, this example might have a resource leak. A program has to do more than rely on the garbage collector (GC) to reclaim a resource's memory when it's finished with it. The program must also release the resoure back to the operating system, typically by calling the resource's close method. However, if a program fails to do this before the GC reclaims the resource, then the information needed to release the resource is lost. The resource, which is still considered by the operaing system to be in use, has leaked.

In this example, if the readLine method throws an exception, and the statement br.close() in the finally block throws an exception, then the FileReader has leaked. Therefore, use a try -with-resources statement instead of a finally block to close your program's resources.

If the methods readLine and close both throw exceptions, then the method readFirstLineFromFileWithFinallyBlock throws the exception thrown from the finally block; the exception thrown from the try block is suppressed. In contrast, in the example readFirstLineFromFile , if exceptions are thrown from both the try block and the try -with-resources statement, then the method readFirstLineFromFile throws the exception thrown from the try block; the exception thrown from the try -with-resources block is suppressed. In Java SE 7 and later, you can retrieve suppressed exceptions; see the section Suppressed Exceptions for more information.

The following example retrieves the names of the files packaged in the zip file zipFileName and creates a text file that contains the names of these files:

In this example, the try -with-resources statement contains two declarations that are separated by a semicolon: ZipFile and BufferedWriter . When the block of code that directly follows it terminates, either normally or because of an exception, the close methods of the BufferedWriter and ZipFile objects are automatically called in this order. Note that the close methods of resources are called in the opposite order of their creation.

The following example uses a try -with-resources statement to automatically close a java.sql.Statement object:

The resource java.sql.Statement used in this example is part of the JDBC 4.1 and later API.

Note : A try -with-resources statement can have catch and finally blocks just like an ordinary try statement. In a try -with-resources statement, any catch or finally block is run after the resources declared have been closed.

Suppressed Exceptions

An exception can be thrown from the block of code associated with the try -with-resources statement. In the example writeToFileZipFileContents , an exception can be thrown from the try block, and up to two exceptions can be thrown from the try -with-resources statement when it tries to close the ZipFile and BufferedWriter objects. If an exception is thrown from the try block and one or more exceptions are thrown from the try -with-resources statement, then those exceptions thrown from the try -with-resources statement are suppressed, and the exception thrown by the block is the one that is thrown by the writeToFileZipFileContents method. You can retrieve these suppressed exceptions by calling the Throwable.getSuppressed method from the exception thrown by the try block.

Classes That Implement the AutoCloseable or Closeable Interface

See the Javadoc of the AutoCloseable and Closeable interfaces for a list of classes that implement either of these interfaces. The Closeable interface extends the AutoCloseable interface. The close method of the Closeable interface throws exceptions of type IOException while the close method of the AutoCloseable interface throws exceptions of type Exception . Consequently, subclasses of the AutoCloseable interface can override this behavior of the close method to throw specialized exceptions, such as IOException , or no exception at all.

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Final variable assignment with try/catch

Because I believe it is a good programming practice, I make all my (local or instance) variables final if they are intended to be written only once.

However, I notice that when a variable assignment can throw an exception you cannot make said variable final:

Is there a way to do this without resorting to a temporary variable? (or is this not the right place for a final modifier?)

2 Answers 2

One way to do this is by introducing a (non- final ) temporary variable, but you said you didn't want to do that.

Another way is to move both branches of the code into a function:

Whether or not this is practical depends on the exact use case.

All in all, as long as x is a an appropriately-scoped local variable, the most practical general approach might be to leave it non- final .

If, on the other hand, x is a member variable, my advice would be to use a non- final temporary during initialization:

No it is not the right place, imagine you got more then 1 Statement in your try and catch block, the first one says : x = 42. After some others Statements the try block fails, and it goes to the catch block, where your Saying x = 30. Now you defined x twice.

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Using try/catch blocks assignment.

Java Try With Resources

Try-with-resources Video

Try-with-resources, try-with-resources java 9 enhancement, closing order, custom autoclosable implementations, catch block, finally block, adding suppressed exceptions manually, resource management with try-catch-finally, old school style.

The Java try with resources construct, AKA Java try-with-resources , is an exception handling mechanism that can automatically close resources like a Java InputStream or a JDBC Connection when you are done with them. To do so, you must open and use the resource within a Java try-with-resources block. When the execution leaves the try-with-resources block, any resource opened within the try-with-resources block is automatically closed, regardless of whether any exceptions are thrown either from inside the try-with-resources block, or when attempting to close the resources.

This Java try-with-resources tutorial explains how the Java try-with-resources construct works, how to properly use it, and how exceptions are handled that are thrown both from inside the try-with-resources block, and during the closing of the resources.

I have created a video version of this Java try-with-resources tutorial, in case you prefer that:

To see how the Java try-with-resources construct work, let us look at a Java try-with-resources example:

This try-with-resources example shows how to open a Java FileInputStream inside a try-with-resources block, read some data from the FileInputStream , and have the FileInputStream closed automatically once execution leaves the try-with-resources block (not explicitly visible).

Notice the first line inside the method in the try-with-resources example above:

This is the try-with-resources construct. The FileInputStream variable is declared inside the parentheses after the try keyword. Additionally, a FileInputStream is instantiated and assigned to the variable.

When the try block finishes the FileInputStream will be closed automatically. This is possible because FileInputStream implements the Java interface java.lang.AutoCloseable . All classes implementing this interface can be used inside the try-with-resources construct.

Before Java 9 a resource that is to be automatically closed must be created inside the parentheses of the try block of a try-with-resources construct. From Java 9, this is no longer necessary. If the variable referencing the resource is effectively final, you can simply enter a reference to the variable inside the try block parentheses. Here is an example of the Java 9 try-with-resources enhancement:

Notice how the input variable is now declared and has a FileInputStream assigned outside the try block. Notice also, how the input variable is references inside the parentheses of the try block. This way, Java will still close it properly once the try block is exited.

Using Multiple Resources

You can use multiple resources inside a Java try-with-resources block and have them all automatically closed. Here is an example of using multiple resources inside a try-with-resources block:

This example creates two resources inside the parentheses after the try keyword. An FileInputStream and a BufferedInputStream . Both of these resources will be closed automatically when execution leaves the try block.

The resources declared in a Java try-with-resources construct will be closed in reverse order of the order in which they are created / listed inside the parentheses. In the example in the previous section, first the will be closed, then the FileInputStream .

The Java try-with-resources construct does not just work with Java's built-in classes. You can also implement the java.lang.AutoCloseable interface in your own classes, and use them with the try-with-resources construct.

The AutoClosable interface only has a single method called close() . Here is how the interface looks:

Any class that implements this interface can be used with the Java try-with-resources construct. Here is a simple example implementation:

The doIt() method is not part of the AutoClosable interface. It is there because we want to be able to do something more than just closing the object.

Here is an example of how the MyAutoClosable is used with the try-with-resources construct:

Here is the output printed to System.out when the method myAutoClosable() is called:

As you can see, try-with-resources is a quite powerful way of making sure that resources used inside a try-catch block are closed correctly, no matter if these resources are your own creation, or Java's built-in components.

Try-with-resources Exception Handling

The exception handling semantics of a Java try-with-resources block vary a bit from the exception handling semantics of a standard Java try-catch-finally block. In most situations the changed semantics will work better for you than the semantics of the original try-catch-finally block, even without you understanding the difference precisely. Even so, it can be a good idea to actually understand what is going on exception handling wise, in the try-with-resources construct. Therefore I will explain the exception handling semantics of the try-with-resources construct here.

If an exception is thrown from within a Java try-with-resources block, any resource opened inside the parentheses of the try block will still get closed automatically. The throwing of the exception will force the execution to leave the try block, and this will force the automatic closing of the resource. The exception thrown from inside the try block will get propagated up the call stack, once the resources have been closed.

Some resources may also throw exceptions when you try to close them. In case a resource throws an exception when you try to close it, any other resources opened within the same try-with-resources block will still get closed. After closing all resources, the exception from the failed close-attempt will get propagated up the call stack. In case multiple exceptions are thrown from multiple resource close attempts, the first exception encountered will be the one propagated up the call stack. The rest of the exceptions will be suppressed.

If an exception is thrown both from inside the try-with-resources block, and when a resource is closed (when close() is called), the exception thrown inside the try block will be propagated up the call stack. The exception thrown when the resource was attempted closed will be suppressed. This is opposite of what happens in a normal try-catch-finally block, where the last exception encountered is the exception that is propagated up the call stack.

To better understand the exception handling semantics of the Java try-with-resources construct, let us look at some examples. For these examples I have created the following AutoClosable implementation which I can force to throw exceptions both when used and when attempted closed:

First, let us look at a basic example with a single resource in use:

In case the second parameter to the AutoClosableResource construct was changed to true , it would throw an exception when attempted closed. In that case, the exception thrown when attempted closed will be propagated up the call stack to the main() method where the try-catch block will catch it. In that case, the Throwable array returned from e.getSuppessed() will be an empty array (size of 0).

In case the parameter to resourceOne.doOp() was changed to true also, the doOp() method would throw an exception. In that case, it is this exception that is propagated up the call stack to the main() method. The exception thrown when attempting to close the resource would be available inside the Throwable array returned by e.getSuppressed() .

Let us look at an example with two AutoClosable resources in use:

In the case where only one of the resources throw an exception, either during use or when attempted closed, the behaviour is the same as when only one resource is used. However, in the example above I have forced both resources to throw an exception when attempted closed, and the first resource to throw an exception when used (when doOp() is called). In that case, the exception thrown from inside the try block is propagated up the call stack. The two exceptions thrown when attempting to close the resources are available in the Throwable array returned by e.getSuppressed() .

Remember, only a single exception can be thrown inside the try block. As soon as an exception is thrown, the try block code is exited, and the resources attempted closed.

You can add a catch block to a try-with-resources block just like you can to a standard try block. If an exception is thrown from within the try block of a try-with-resources block, the catch block will catch it, just like it would when used with a standard try construct.

Before the catch block is entered, the try-with-resources construct will attempt to close the resources opened inside the try block. In case an exception is thrown when attempting to close one of the resources, these exceptions will be available from the exception's getSuppressed() method inside the catch block. Here is an example of a Java try-with-resources block with a catch block attached:

In the example above, the AutoClosableResource is configured to throw an exception both when doOp() is called, and when it is attempted closed (via close() ). The exception thrown from doOp() is caught in the catch block, its getSuppressed() method returns an array with the exception thrown when the resource was attempted closed.

In case that an exception is only thrown when the resource is attempted closed, the catch block will also catch it. The getSuppressed() method of that exception will return an empty array, since no exceptions where suppressed.

It is also possible to add a finally block to a Java try-with-resources block. It will behave just like a standard finally block, meaning it will get executed as the last step before exiting the try-with-resources block - after any catch block has been executed.

In case you throw an exception from within the finally block of a try-with-resources construct, all previously thrown exceptions will be lost! Here is an example of throwing an exception from within the finally block of a Java try-with-resources construct:

Notice, that the exception thrown from within the catch block will be ignored because a new exception is thrown from within the finally block. This would also be true if there was no catch block. Then any exception thrown from inside the try block would get lost because a new exception is thrown from inside the finally block. Any previous exceptions are not suppressed, so they are not available from within the exception thrown from the finally block.

The Throwable class has a method named addSuppressed() which takes a Throwable object as parameter. Using the addSuppressed() method it is possible to add suppressed exceptions to another exception, in case you need that. Here is an example that shows how to add suppressed exceptions to a Java exception manually:

Notice how the Throwable reference has to be declared outside the try-with-resources construct. Otherwise the catch and finally blocks cannot access it.

In most cases you will not need to add suppressed exceptions to an exception manually, but now you have at least seen how it can be done, in case you ever run into a situation where you need it.

The Java try-with-resources construct was added in Java 7. Managing resources that need to be explicitly closed was somewhat tedious before Java 7. You had to handle the correct closure of the resources manually. This was not an easy task to handle correctly. To understand why, look at the following method which reads a file and prints it to the System.out :

The code marked in bold is where the code can throw an Exception . As you can see, that can happen in 3 places inside the try -block, and 1 place inside the finally -block.

The finally block is always executed no matter if an exception is thrown from the try block or not. That means, that the InputStream is closed no matter what happens in the try block. Or, attempted closed that is. The InputStream 's close() method may throw an exception too, if closing it fails.

Imagine that an exception is thrown from inside the try block. Then the finally block is executed. Imagine then, that an exception is also thrown from the finally block. Which exception do you think is propagated up the call stack?

The exception thrown from the finally block would be propagated up the call stack, even if the exception thrown from the try block would probably be more relevant to propagate.

java try assignment

Related Articles

Try-with-resources Feature in Java

In Java, the Try-with-resources statement is a try statement that declares one or more resources in it. A resource is an object that must be closed once your program is done using it. For example, a File resource or a Socket connection resource. The try-with-resources statement ensures that each resource is closed at the end of the statement execution. If we don’t close the resources, it may constitute a resource leak and also the program could exhaust the resources available to it.

You can pass any object as a resource that implements java.lang.AutoCloseable , which includes all objects which implement java.io.Closeable.

By this, now we don’t need to add an extra finally block for just passing the closing statements of the resources. The resources will be closed as soon as the try-catch block is executed.

Syntax: Try-with-resources

When it comes to exceptions, there is a difference in try-catch-finally block and try-with-resources block. If an exception is thrown in both try block and finally block, the method returns the exception thrown in finally block.

For try-with-resources, if an exception is thrown in a try block and in a try-with-resources statement, then the method returns the exception thrown in the try block. The exceptions thrown by try-with-resources are suppressed, i.e. we can say that try-with-resources block throws suppressed exceptions.

Now, let us discuss both the possible scenarios which are demonstrated below as an example as follows:

Example 1: try-with-resources having a single resource

Example 2: try-with-resources having multiple resources

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In this tutorial, we will learn about the try catch statement in Java with the help of examples.

The try...catch block in Java is used to handle exceptions and prevents the abnormal termination of the program.

Here's the syntax of a try...catch block in Java.

The try block includes the code that might generate an exception.

The catch block includes the code that is executed when there occurs an exception inside the try block.

Example: Java try...catch block

In the above example, notice the line,

Here, we are trying to divide a number by zero . In this case, an exception occurs. Hence, we have enclosed this code inside the try block.

When the program encounters this code, ArithmeticException occurs. And, the exception is caught by the catch block and executes the code inside the catch block.

The catch block is only executed if there exists an exception inside the try block.

Note : In Java, we can use a try block without a catch block. However, we cannot use a catch block without a try block.

Java try...finally block

We can also use the try block along with a finally block.

In this case, the finally block is always executed whether there is an exception inside the try block or not.

Example: Java try...finally block

In the above example, we have used the try block along with the finally block. We can see that the code inside the try block is causing an exception.

However, the code inside the finally block is executed irrespective of the exception.

Java try...catch...finally block

In Java, we can also use the finally block after the try...catch block. For example,

In the above example, we have created an array named list and a file named output.txt . Here, we are trying to read data from the array and storing to the file.

Notice the code,

Here, the size of the array is 5 and the last element of the array is at list[4] . However, we are trying to access elements at a[5] and a[6] .

Hence, the code generates an exception that is caught by the catch block.

Since the finally block is always executed, we have included code to close the PrintWriter inside the finally block.

It is a good practice to use finally block to include important cleanup code like closing a file or connection.

Note : There are some cases when a finally block does not execute:

For each try block, there can be zero or more catch blocks. Multiple catch blocks allow us to handle each exception differently.

The argument type of each catch block indicates the type of exception that can be handled by it. For example,

In this example, we have created an integer array named arr of size 10 .

Since the array index starts from 0 , the last element of the array is at arr[9] . Notice the statement,

Here, we are trying to assign a value to the index 10 . Hence, IndexOutOfBoundException occurs.

When an exception occurs in the try block,

From Java SE 7 and later, we can now catch more than one type of exception with one catch block.

This reduces code duplication and increases code simplicity and efficiency.

Each exception type that can be handled by the catch block is separated using a vertical bar | .

To learn more, visit Java catching multiple exceptions .

Java try-with-resources statement

The try-with-resources statement is a try statement that has one or more resource declarations.

The resource is an object to be closed at the end of the program. It must be declared and initialized in the try statement.

Let's take an example.

The try-with-resources statement is also referred to as automatic resource management . This statement automatically closes all the resources at the end of the statement.

To learn more, visit the java try-with-resources statement .

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java try assignment

1.4. Expressions and Assignment Statements ¶

In this lesson, you will learn about assignment statements and expressions that contain math operators and variables.

1.4.1. Assignment Statements ¶

Remember that a variable holds a value that can change or vary. Assignment statements initialize or change the value stored in a variable using the assignment operator = . An assignment statement always has a single variable on the left hand side of the = sign. The value of the expression on the right hand side of the = sign (which can contain math operators and other variables) is copied into the memory location of the variable on the left hand side.

Assignment statement

Figure 1: Assignment Statement (variable = expression) ¶

Instead of saying equals for the = operator in an assignment statement, say “gets” or “is assigned” to remember that the variable on the left hand side gets or is assigned the value on the right. In the figure above, score is assigned the value of 10 times points (which is another variable) plus 5.

The following video by Dr. Colleen Lewis shows how variables can change values in memory using assignment statements.

As we saw in the video, we can set one variable to a copy of the value of another variable like y = x;. This won’t change the value of the variable that you are copying from.

coding exercise

Click on the Show CodeLens button to step through the code and see how the values of the variables change.

The program is supposed to figure out the total money value given the number of dimes, quarters and nickels. There is an error in the calculation of the total. Fix the error to compute the correct amount.

Calculate and print the total pay given the weekly salary and the number of weeks worked. Use string concatenation with the totalPay variable to produce the output Total Pay = $3000 . Don’t hardcode the number 3000 in your print statement.

Assume you have a package with a given height 3 inches and width 5 inches. If the package is rotated 90 degrees, you should swap the values for the height and width. The code below makes an attempt to swap the values stored in two variables h and w, which represent height and width. Variable h should end up with w’s initial value of 5 and w should get h’s initial value of 3. Unfortunately this code has an error and does not work. Use the CodeLens to step through the code to understand why it fails to swap the values in h and w.

1-4-7: Explain in your own words why the ErrorSwap program code does not swap the values stored in h and w.

Swapping two variables requires a third variable. Before assigning h = w , you need to store the original value of h in the temporary variable. In the mixed up programs below, drag the blocks to the right to put them in the right order.

The following has the correct code that uses a third variable named “temp” to swap the values in h and w.

The code is mixed up and contains one extra block which is not needed in a correct solution. Drag the needed blocks from the left into the correct order on the right, then check your solution. You will be told if any of the blocks are in the wrong order or if you need to remove one or more blocks.

After three incorrect attempts you will be able to use the Help Me button to make the problem easier.

Fix the code below to perform a correct swap of h and w. You need to add a new variable named temp to use for the swap.

1.4.2. Incrementing the value of a variable ¶

If you use a variable to keep score you would probably increment it (add one to the current value) whenever score should go up. You can do this by setting the variable to the current value of the variable plus one (score = score + 1) as shown below. The formula looks a little crazy in math class, but it makes sense in coding because the variable on the left is set to the value of the arithmetic expression on the right. So, the score variable is set to the previous value of score + 1.

Click on the Show CodeLens button to step through the code and see how the score value changes.

1-4-11: What is the value of b after the following code executes?

1-4-12: What are the values of x, y, and z after the following code executes?

1.4.3. Operators ¶

Java uses the standard mathematical operators for addition ( + ), subtraction ( - ), multiplication ( * ), and division ( / ). Arithmetic expressions can be of type int or double. An arithmetic operation that uses two int values will evaluate to an int value. An arithmetic operation that uses at least one double value will evaluate to a double value. (You may have noticed that + was also used to put text together in the input program above – more on this when we talk about strings.)

Java uses the operator == to test if the value on the left is equal to the value on the right and != to test if two items are not equal. Don’t get one equal sign = confused with two equal signs == ! They mean different things in Java. One equal sign is used to assign a value to a variable. Two equal signs are used to test a variable to see if it is a certain value and that returns true or false as you’ll see below. Use == and != only with int values and not doubles because double values are an approximation and 3.3333 will not equal 3.3334 even though they are very close.

Run the code below to see all the operators in action. Do all of those operators do what you expected? What about 2 / 3 ? Isn’t surprising that it prints 0 ? See the note below.

When Java sees you doing integer division (or any operation with integers) it assumes you want an integer result so it throws away anything after the decimal point in the answer, essentially rounding down the answer to a whole number. If you need a double answer, you should make at least one of the values in the expression a double like 2.0.

With division, another thing to watch out for is dividing by 0. An attempt to divide an integer by zero will result in an ArithmeticException error message. Try it in one of the active code windows above.

Operators can be used to create compound expressions with more than one operator. You can either use a literal value which is a fixed value like 2, or variables in them. When compound expressions are evaluated, operator precedence rules are used, so that *, /, and % are done before + and -. However, anything in parentheses is done first. It doesn’t hurt to put in extra parentheses if you are unsure as to what will be done first.

In the example below, try to guess what it will print out and then run it to see if you are right. Remember to consider operator precedence .

1-4-15: Consider the following code segment. Be careful about integer division.

What is printed when the code segment is executed?

1-4-16: Consider the following code segment.

What is the value of the expression?

1-4-17: Consider the following code segment.

1-4-18: Consider the following code segment.

1.4.4. The Modulo Operator ¶

The percent sign operator ( % ) is the mod (modulo) or remainder operator. The mod operator ( x % y ) returns the remainder after you divide x (first number) by y (second number) so 5 % 2 will return 1 since 2 goes into 5 two times with a remainder of 1. Remember long division when you had to specify how many times one number went into another evenly and the remainder? That remainder is what is returned by the modulo operator.

../_images/mod-py.png

Figure 2: Long division showing the whole number result and the remainder ¶

In the example below, try to guess what it will print out and then run it to see if you are right.

The result of x % y when x is smaller than y is always x . The value y can’t go into x at all (goes in 0 times), since x is smaller than y , so the result is just x . So if you see 2 % 3 the result is 2 .

1-4-21: What is the result of 158 % 10?

1-4-22: What is the result of 3 % 8?

1.4.5. FlowCharting ¶

Assume you have 16 pieces of pizza and 5 people. If everyone gets the same number of slices, how many slices does each person get? Are there any leftover pieces?

In industry, a flowchart is used to describe a process through symbols and text. A flowchart usually does not show variable declarations, but it can show assignment statements (drawn as rectangle) and output statements (drawn as rhomboid).

The flowchart in figure 3 shows a process to compute the fair distribution of pizza slices among a number of people. The process relies on integer division to determine slices per person, and the mod operator to determine remaining slices.

Figure 3: Example Flow Chart ¶

A flowchart shows pseudo-code, which is like Java but not exactly the same. Syntactic details like semi-colons are omitted, and input and output is described in abstract terms.

Complete the program based on the process shown in the Figure 3 flowchart. Note the first line of code declares all 4 variables as type int. Add assignment statements and print statements to compute and print the slices per person and leftover slices. Use System.out.println for output.

1.4.6. Storing User Input in Variables ¶

Variables are a powerful abstraction in programming because the same algorithm can be used with different input values saved in variables.

Program input and output

Figure 4: Program input and output ¶

A Java program can ask the user to type in one or more values. The Java class Scanner is used to read from the keyboard input stream, which is referenced by System.in . Normally the keyboard input is typed into a console window, but since this is running in a browser you will type in a small textbox window displayed below the code. The code below shows an example of prompting the user to enter a name and then printing a greeting. The code String name = scan.nextLine() gets the string value you enter as program input and then stores the value in a variable.

Run the program a few times, typing in a different name. The code works for any name: behold, the power of variables!

Run this program to read in a name from the input stream. You can type a different name in the input window shown below the code.

Try stepping through the code with the CodeLens tool to see how the name variable is assigned to the value read by the scanner. You will have to click “Hide CodeLens” and then “Show in CodeLens” to enter a different name for input.

The Scanner class has several useful methods for reading user input. A token is a sequence of characters separated by white space.

Run this program to read in an integer from the input stream. You can type a different integer value in the input window shown below the code.

A rhomboid (slanted rectangle) is used in a flowchart to depict data flowing into and out of a program. The previous flowchart in Figure 3 used a rhomboid to indicate program output. A rhomboid is also used to denote reading a value from the input stream.

Figure 5: Flow Chart Reading User Input ¶

Figure 5 contains an updated version of the pizza calculator process. The first two steps have been altered to initialize the pizzaSlices and numPeople variables by reading two values from the input stream. In Java this will be done using a Scanner object and reading from System.in.

Complete the program based on the process shown in the Figure 5 flowchart. The program should scan two integer values to initialize pizzaSlices and numPeople. Run the program a few times to experiment with different values for input. What happens if you enter 0 for the number of people? The program will bomb due to division by zero! We will see how to prevent this in a later lesson.

The program below reads two integer values from the input stream and attempts to print the sum. Unfortunately there is a problem with the last line of code that prints the sum.

Run the program and look at the result. When the input is 5 and 7 , the output is Sum is 57 . Both of the + operators in the print statement are performing string concatenation. While the first + operator should perform string concatenation, the second + operator should perform addition. You can force the second + operator to perform addition by putting the arithmetic expression in parentheses ( num1 + num2 ) .

More information on using the Scanner class can be found here https://www.w3schools.com/java/java_user_input.asp

1.4.7. Programming Challenge : Dog Years ¶

In this programming challenge, you will calculate your age, and your pet’s age from your birthdates, and your pet’s age in dog years. In the code below, type in the current year, the year you were born, the year your dog or cat was born (if you don’t have one, make one up!) in the variables below. Then write formulas in assignment statements to calculate how old you are, how old your dog or cat is, and how old they are in dog years which is 7 times a human year. Finally, print it all out.

Calculate your age and your pet’s age from the birthdates, and then your pet’s age in dog years. If you want an extra challenge, try reading the values using a Scanner.

1.4.8. Summary ¶

Arithmetic expressions include expressions of type int and double.

The arithmetic operators consist of +, -, * , /, and % (modulo for the remainder in division).

An arithmetic operation that uses two int values will evaluate to an int value. With integer division, any decimal part in the result will be thrown away, essentially rounding down the answer to a whole number.

An arithmetic operation that uses at least one double value will evaluate to a double value.

Operators can be used to construct compound expressions.

During evaluation, operands are associated with operators according to operator precedence to determine how they are grouped. (*, /, % have precedence over + and -, unless parentheses are used to group those.)

An attempt to divide an integer by zero will result in an ArithmeticException to occur.

The assignment operator (=) allows a program to initialize or change the value stored in a variable. The value of the expression on the right is stored in the variable on the left.

During execution, expressions are evaluated to produce a single value.

The value of an expression has a type based on the evaluation of the expression.

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