Programs need to be able to react differently to varying data. Conditional statements let us do this. For example, a robot must be able to monitor its sensors to prevent collisions. Consider (and try running) the following program:

1. Create a new folder in your Java Projects folder named Conditional Example
2. Create a new file (New->File)
3. Cut and paste this program into the file.

   public class ConditionalExample {
       public static void main(String args[]) {
           int rangeInInches;
   
           rangeInInches = 10;
   
           if (rangeInInches < 20) {
              System.out.println("stop motors so we don't crash!");
           } else {
              System.out.println("full speed ahead!");
           }
       }
   }
   

4. Save the program as ConditionalExample.java (notice how the name of the file must match the name of the class)

Running the program

Run the program using the debugger with a breakpoint set on the first executable line (rangeInInches=10);

• Step through the program using the stepover tool and observe the flow of the program.
• Restart the program using the restart tool
• Change the values stored in the variable rangeInInches to 25 and observe the flow of the program.

Extra Credit

Java allows you to have multiple conditionals using the syntax:

     if (<condition 1>) {
        // do this if condition 1 is true
        // also do this if condition 1 is true
     } else if (<condition 2>) {
        // do this if condition 1 was not true but condition 2 is true
     } else {
        // do this if neither condition 1 nor condition 2 were true
     }

You can have as many else if clauses as you wish.

• Try adding an else if clause to the sample program.

Some things to note:

• The conditions are always placed within parentheses
• The conditions are logic statements that must evaluate to true or false (e.g. (a < 10))
• The conditions are evaluated in order and the first condition that matches is executed, the rest are skipped
• The else if and else clauses are optional