| 4. 4. 1. While语句 |
|
|
- One way to create a loop is by using the while statement.
- Another way is to use the for statement
|
The while statement has the following syntax. |
|
while (booleanExpression) {
statement (s)
}
|
|
- statement(s) will be executed as long as booleanExpression evaluates to true.
- If there is only a single statement inside the braces, you may omit the braces.
- For clarity, you should always use braces even when there is only one statement.
|
As an example of the while statement, the following code prints integer numbers that
are less than three. |
|
public class MainClass {
public static void main(String[] args) {
int i = 0;
while (i < 3) {
System.out.println(i);
i++;
}
}
}
|
|
To produce three beeps with an interval of 500 milliseconds, use this code: |
|
public class MainClass {
public static void main(String[] args) {
int j = 0;
while (j < 3) {
java.awt.Toolkit.getDefaultToolkit().beep();
try {
Thread.currentThread().sleep(500);
} catch (Exception e) {
}
j++;
}
}
}
|
|
Sometimes, you use an expression that always evaluates to true (such as the boolean literal
true) but relies on the break statement to escape from the loop. |
|
public class MainClass {
public static void main(String[] args) {
int k = 0;
while (true) {
System.out.println(k);
k++;
if (k > 2) {
break;
}
}
}
}
|
|