The do-while construct is a loop structure which repeatedly executes one or some statements until a condition becomes false. In other words, it repeats the statements while the condition is still true.

 

1. Syntax of do...while construct in Java:

The first form (there is only while keyword):

while (condition is true) {
    // statements
}

 

The second form (there are both do and while keywords):

do {
    // statements
} while (condition is true); 

 

2. Some Rules about do...while construct in Java:

• • The while construct starts executing the statements in its body only if the condition is true. The statements may not be executed (if condition is false from start).
  • The do-while construct always execute the statements in its body at least one time, even if the condition is false from start.
  • If there is only one statement in the body, the curly braces can be removed.

 

3. Java do..while Examples

The following code uses a while loop prints out 10 numbers from 1 to 10:

int i = 1;
while (i <= 10) {
    System.out.println(i);
    i++;
} 

The following do-while loop reads input from command line until an empty string is entered:

String input = null;
do {
    System.out.print("Enter input: ");
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    input = reader.readLine();
    System.out.println("Your input: " + input);
} while (!input.equals(""));

 

Related Tutorials:

• Java for loop construct
• All keywords in Java
• Summary of primitive data types in Java
• Summary of operators in Java with examples

 

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