How to use Java conditional statements effectively

Working with if, else and switch statements

The Java language provides three constructs for performing conditional logic:

1. The if statement
2. The else statement
3. The switch statement

It's often asserted that Java has an additional else...if statement, which isn't technically true. You can nest if statements inside of an else block, and the code to do so puts the else and if statements right next to each other, but that's just happenstance. The else...if statement isn't a special Java construct in itself.

The syntax for an if…else statement looks like this:

if (boolean condition) {

} else {

}

The first code block executes if the boolean condition is true, and the second code block executes if the boolean condition is false. Here's how the rock-paper-scissors (or roshambo) application would look if we introduced the else keyword into the mix.

import javax.swing.*;

public class Roshambo {

     public static void main(String args[]) {

           String prompt = "Will it be rock, paper or scissors?";

           String clientGesture = null;

           String serverGesture = "rock";

           String outcome = "error";

           clientGesture = JOptionPane.showInputDialog(prompt);

           if (clientGesture.equalsIgnoreCase("rock")) {

                outcome = "tie";

           } else if (clientGesture.equalsIgnoreCase("scissors")) {

                outcome = "loss";

           } else     if (clientGesture.equalsIgnoreCase("paper")) {

                outcome = "win";

           }

           JOptionPane.showMessageDialog(null, outcome);

     }

}

When the code is run, the UI looks exactly the same as before, although the implementation is now much cleaner and more efficient (Figure 1).

Figure 1. Swing-based components providing a UI for the roshambo application.

Working with Java's switch statement

Another of the Java conditional statements, the switch statement, can be useful when a variety of different conditions might be true based on the value of a single char, integer or a String. With the roshambo application, the clientGesture String can take on the values of rock, paper or scissors, and depending upon which is selected, the variable named outcome is assigned a different value. This is a perfect scenario for using a switch statement. Replacing the if-based conditional logic in the current application with a switch would look like this:

import javax.swing.*;

public class Roshambo {

     public static void main(String args[]) {

           String prompt = "Will it be rock, paper or scissors?";

           String clientGesture = null;

           String serverGesture = "rock";

           String outcome = "error";

           clientGesture = JOptionPane.showInputDialog(prompt);

           switch (clientGesture) {

                case "rock":

                     outcome = "tie";

                     break;

                case "paper":

                     outcome= "win";

                     break;

                case "scissors":

                     outcome = "loss";

                     break;

                default:

                     outcome="error";

           }

           JOptionPane.showMessageDialog(null, outcome);

     }

}

A few points about the switch

A few things to know about the switch statement:

• Only since Java 7 has it been possible to switch on String values
• Once a condition is met, all subsequent conditions are executed unless a break statement is used to exit the switch block
• An optional default block can be used as a catch-all to handle the situation where none of the predicted conditions are met

In the grand scheme of things, all computer programs come down to three key processes:

1. Handling data through variables
2. Conditional logic
3. Iterative looping

As mentioned earlier, only three constructs in Java pertain to performing conditional logic: the if, else and switch statements. Once you have mastered them, you have mastered the art of using Java conditional statements.

Which software development language do you think compliments Java the most? Let us know.