Session 5 Lecture Notes for First Course in Java
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Selection Statements

if

    if( boolean expression ) {
        statement1;
        ...
        statementn;
    } 

Note: Curly braces only required if there is more than one execution statement.

If..else

    if( x == y ) {
      // do this
    } else {
      // do this
    }

Note: The "else" is for the last statement. 

If..else if .. else

    if( x == y ) {
      // do this
    } else if( x > y ) {        // nested 'if'
      // do this
      // Note: any number of "else if" clauses after "if" and before "else"
    } else {
      // do this
    }

Note: The "else" is for the last statement. 

The output is:

x not > or = to y

switch

The output is:

On Monday my wallet contained $25
I'll spend $5 on Monday for lunch
I have $20 to spend on lunch for the rest of the week

On Tuesday my wallet contained $20
I'll spend $6 on Tuesday for lunch
I have $14 to spend on lunch for the rest of the week

On Wednesday my wallet contained $14
I'll spend $6 on Wednesday for lunch
I have $8 to spend on lunch for the rest of the week

On Thursday my wallet contained $8
I'll spend $8 on Thursday for lunch
I have $0 to spend on lunch for the rest of the week

On Friday my wallet contained $0
I'll spend $3 on Friday for lunch
I have $-3 to spend on lunch for the rest of the week

If I want to eat the rest of the week I better
visit my friendly neighborhood ATM!

Iteration Statements

while

A while loop:

• is more simple than a for loop
• is equivalent to a for loop in terms of work it can do (rewritability)
• tests a boolean expression contained inside parentheses

The output of the while loop is equivalent to that of the corresponding for loop:

96 is a multiple of 8
88 is a multiple of 8
80 is a multiple of 8
72 is a multiple of 8
64 is a multiple of 8
56 is a multiple of 8
48 is a multiple of 8
40 is a multiple of 8
32 is a multiple of 8
24 is a multiple of 8
16 is a multiple of 8
8 is a multiple of 8

The while loop above is a pre-test loop because it evaluates the boolean expression in line 14 before executing lines 15-17.

do-while

The do while loop is a post-test.

The test in a post-test loop is at the end of the loop.

We saw this last week in do .. while.

for

We saw this in scope in a for loop example

nested loops

outer loop value i = 0
    j = 0
    j = 1
    j = 2
    j = 3
    j = 4

outer loop value i = 1
    j = 1
    j = 2
    j = 3
    j = 4

outer loop value i = 2
    j = 2
    j = 3
    j = 4

outer loop value i = 3
    j = 3
    j = 4

outer loop value i = 4
    j = 4

Jump Statements

break

The break statement causes execution to exit the current loop.
In this example, the break occurs in an inner loop, but the outer loop remains unaffected.

The output is:

Pass 0: 0 1 2 3 4 5 6 7 8 9
Pass 1: 0 1 2 3 4 5 6 7 8 9
Pass 2: 0 1 2 3 4 5 6 7 8 9
Loops complete.

continue

This example uses the continue statement to force iteration to continue as long as the boolean test results in true.
What operators does the boolean test use? I

The output is:

0 1
2 3
4 5
6 7
8 9

Here's a more complex use of  the continue statement:

The output is:

0
0 1
0 2 4
0 3 6 9
0 4 8 12 16
0 5 10 15 20 25
0 6 12 18 24 30 36
0 7 14 21 28 35 42 49
0 8 16 24 32 40 48 56 64
0 9 18 27 36 45 54 63 72 81

Homework Assignment

Let's go on to objects and get our homework from that lecture.

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