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Java Ternary Operator Control Statement

By Stephen Bucaro

A computer program is a list of instructions for the computer to follow. Some instructions tell the computer to test a variable and to follow a group of instructions based on the result of that test. This type of instruction is called a conditional test.

The ternary operator (?) is often confusing to beginners. The ternary operator is used to assign one of two values to a variable based on a conditional test.

Ternary Operator Syntax

result = condition ? value1 : value2

This statement means if condition is true, then assign the value1 to result; otherwise, assign the value2 to result.

Below is example code using the ternary operator:

import javax.swing.*;

public class ternaryOper
{
   public static void main(String s[])
   {
      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
      frame.setSize(300,300);
      frame.setLocationRelativeTo(null);
      frame.setTitle("Java ifelse Test");

      int height = 70;

      JTextArea myText = new JTextArea();
      myText.setLineWrap(true);

      String tall = (height < 72) ? "Your height is too short." : "Your height is tall enough.";

      myText.append(tall);
      frame.add(myText);

      frame.setVisible(true);
   }
}

In the code shown above, the value stored in height is tested to see if it's less-than 72. If the test result is true, the string "Your height is too short." is assigned to the String object tall. If the test result is false, the string "Your height is tall enough." is assigned to tall.

Note: I generally hate it when people add a bunch of extra code to an example. It confuses things. But in this case I've included the javax.swing library and added code to create a JFrame and a JTextArea. If I didn't add this extra code, you would need to use the System.out.print command to output text, and I don't think that's an interesting or realistic way to learn Java programming.

In the code above, a JTextArea object named myTextis created, and the line myText.append(tall) places the tall string in the JTextArea for display in the program window.

If you're a beginner, for this example, I recommend downloading and installing the Java Development Kit from Oracle's web site. Type the code into a text file using a basic text editor like Window's Notepad (Do not use a word processor because they insert formatting codes into the file), saving the file with the .java file extension. Then use a batch file to compile the program. The batch file needs to contain the path to the compiler and the path to the source file, an example of compile.bat is shown below.

c:\Program Files\java\jdk1.8.0_121\bin\javac c:\Users\Stephen\Desktop\program_name.java
pause

The pause command on the second line will cause the DOS shell to stay open until you press any key, allowing you to read any errors. If successful, the compiler will create an executable file with the .class file extension. Then use a batch file to run the program. The batch file needs to contain the start command, the name of the java program launcher, and the name of the compiled java class file (without the .class extension). An example of run.bat is shown below.