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Trail: Learning the Java Language
Lesson: Language Basics
Section: Control Flow Statements
Language Basics
Variables
Primitive Data Types
Arrays
Summary of Variables
Questions and Exercises
Operators
Assignment, Arithmetic, and Unary Operators
Equality, Relational, and Conditional Operators
Bitwise and Bit Shift Operators
Summary of Operators
Questions and Exercises
Expressions, Statements, and Blocks
Questions and Exercises
Control Flow Statements
The if-then and if-then-else Statements
The switch Statement
The while and do-while Statements
The for Statement
Branching Statements
Summary of Control Flow Statements
Questions and Exercises
Home Page > Learning the Java Language > Language Basics
The while and do-while Statements

> The `while` statement continually executes a block of statements while a particular condition is `true`. Its syntax can be expressed as:

> >     while (expression) {
> >          statement(s)
> >     }

> The `while` statement evaluates expression, which must return a `boolean` value. If the expression evaluates to `true`, the `while` statement executes the statement(s) in the `while` block. The `while` statement continues testing the expression and executing its block until the expression evaluates to `false`. Using the `while` statement to print the values from 1 through 10 can be accomplished as in the following `WhileDemo` program:

> >     class WhileDemo {
> >          public static void main(String[] args){
> >               int count = 1;
> >               while (count < 11) {
> >                    System.out.println("Count is: " + count);
> >                    count++;
> >               }
> >          }
> >     }

> You can implement an infinite loop using the `while` statement as follows:

> >     while (true){
> >         // your code goes here
> >     }

> The Java programming language also provides a `do-while` statement, which can be expressed as follows:

> >     do {
> >          statement(s)
> >     } while (expression);

> The difference between `do-while` and `while` is that `do-while` evaluates its expression at the bottom of the loop instead of the top. Therefore, the statements within the `do` block are always executed at least once, as shown in the following `DoWhileDemo` program:

> >     class DoWhileDemo {
> >          public static void main(String[] args){
> >               int count = 1;
> >               do {
> >                    System.out.println("Count is: " + count);
> >                    count++;
> >               } while (count <= 11);
> >          }
> >     }

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