do-while statement
To execute the body of a while loop at least once, you can use the do-while loop. Its general form is
do {
// body of loop
} while (condition);
Here is an example to show how to use a do-while loop.
It generates the same output as before.
public class Main {
public static void main(String args[]) {
int n = 10;
do {
System.out.println("n:" + n);
n--;
} while (n > 0);
}
}
The loop in the preceding program can be written as follows:
n:10
n:9
n:8
n:7
n:6
n:5
n:4
n:3
n:2
n:1
public class Main {
public static void main(String args[]) {
int n = 10;
do {
System.out.println("n:" + n);
} while (--n > 0);
}
}
The output:
n:10
n:9
n:8
n:7
n:6
n:5
n:4
n:3
n:2
n:1
The following program implements a very simple help system with do-while loop and switch statement.
public class Main {
public static void main(String args[]) throws java.io.IOException {
char choice;
do {
System.out.println("Help on:");
System.out.println(" 1. A");
System.out.println(" 2. B");
System.out.println(" 3. C");
System.out.println(" 4. D");
System.out.println(" 5. E");
System.out.println("Choose one:");
choice = (char) System.in.read();
} while (choice < '1' || choice > '5');
System.out.println("\n");
switch (choice) {
case '1':
System.out.println("A");
break;
case '2':
System.out.println("B");
break;
case '3':
System.out.println("C");
break;
case '4':
System.out.println("D");
break;
case '5':
System.out.println("E");
break;
}
}
}
Here is a sample run produced by this program:
Help on:
1. A
2. B
3. C
4. D
5. E
Choose one: