Java 天地·Core Java·Lecture Notes·Unitt4 - Control of execution

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Iteration: FOR

Aforstatement works in a very similar way to an whilestatement. However, forstatements
are particularly useful for concisely writing counter controlled loops.

The general form of aforstatement can be illustrated as:

for( <loop initialise>; <loop condition>; <post loop action>)
{
<actions to perform if loop condition is true>

}

The way aforloop works is as follows:

first the <loop initialise> statement is executed
then the loop condition is tested
if the loop condition is true
the loop actions are performed
the post loop action is performed
the loop condition is tested again and so on
once the loop condition is found to be false, the loop terminates

An example of awhile loop, and its equivalent for loop are as follows:

// a WHILE loop

int counter = 0;

while( counter < 10 )
{
<action1>
<action2>
counter = counter + 1;
}

// an equivalent FOR loop

int counter;

for( counter = 0; counter < 10; counter = counter + 1)
{
<action1>
<action2>
}

As can be seen, for counter controlled loops such as the above, the for loop is neater, since it moves the post loop action of incrementing the counter inside the loop definition line.

The table below illustrates what happens when this for loop is executed:

As the for loop iterates the following happens:

counter	loop condition	<action1> <action2>	post loop action: counter = counter + 1
0	0 < 10 = true	actions 1 and 2 are executed	counter= 0 + 1 = 1
1	1 < 10 = true	actions 1 and 2 are executed	counter = 1 + 1 = 2
2	2 < 10 = true	actions 1 and 2 are executed	counter = 2 + 1 = 3
3	3 < 10 = true	actions 1 and 2 are executed	counter = 3 + 1= 4
...	... < 10	actions 1 and 2 are executed	counter = counter + 1
9	9 <10 = true	actions 1 and 2 are executed	counter = 9 + 1= 10
10		10 < 10= false loop terminates

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