If-statements & Indefinite Loops

1. If-statements & Indefinite Loops CSE 115 Spring 2006 April 24, 26, & 28 2006

2. Selection • Choice in a program. • We’ve seen polymorphism already as a mechanism for a way for a program to behave differently under different conditions. • There is another construct for selection built into Java: if-statements.

3. If-statements • Syntax if (booleanExpression) { //code executed if boolean //Expression is true }

4. If-else statements if (booleanExpression) { //code executed if boolean //Expression is true } else { //code executed if boolean //Expression is false }

5. If-else statements (more than two choices) if (booleanExpression1) { //code executed if boolean //Expression1 is true } else if (booleanExpression2) { //code executed if boolean //Expression2 is true } else { //code executed if neither boolean //Expression1 or booleanExpression2 is //true }

6. Loops (Iteration/Repetition) • The ability to do a task repeatedly. • The functionality of repetition is most often implemented in programming languages using loops.

7. Indefinite Loop • There are two types of indefinite loops built into Java, the while-loop and the do-while-loop. An indefinite loop is normally used when you do not know how many times you want a specific task to be performed.

8. Entry vs. Exit Test Loop • A “while-loop” is also characterized as an entry-test loop (like the for-loop). That is, a condition about whether the loop should continue is tested before actually doing the work of the loop. • A “do-while-loop” is an exit-test loop. That is, the work of the loop is done before the condition is tested about whether the loop should continue.

9. Syntax of while-loop while (booleanExpression) { //loop body } • Essentially, keep looping until the condition is false.

10. Syntax of do-while-loop Do { //loop body } while (booleanExpression); • Essentially, do it once and then keep looping until the condition is false.

11. The equals method • The == operator does not always give us the desired results when comparing two objects (non-primitives). • We need to use the equals method to obtain information about object equality. • All classes inherit this method from java.lang.Object, but need to override it to perform as appropriate.

12. The toString method • Another method inherited from java.lang.Object that should be overridden to perform appropriately for each object. • This method gives a String representation of an object that can be printed out to the console using System.out.println statements.