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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 for Statement

> The `for` statement provides a compact way to iterate over a range of values. Programmers often refer to it as the "for loop" because of the way in which it repeatedly loops until a particular condition is satisfied. The general form of the `for` statement can be expressed as follows:

> >     for (initialization; termination; increment) {
> >         statement(s)
> >     }

> When using this version of the `for` statement, keep in mind that:
> - The initialization expression initializes the loop; it's executed once, as the loop begins.
> - When the termination expression evaluates to `false`, the loop terminates.
> - The increment expression is invoked after each iteration through the loop; it is perfectly acceptable for this expression to increment or decrement a value.

> The following program, `ForDemo`, uses the general form of the `for` statement to print the numbers 1 through 10 to standard output:

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

> The output of this program is:

> >     Count is: 1
> >     Count is: 2
> >     Count is: 3
> >     Count is: 4
> >     Count is: 5
> >     Count is: 6
> >     Count is: 7
> >     Count is: 8
> >     Count is: 9
> >     Count is: 10

> Notice how the code declares a variable within the initialization expression. The scope of this variable extends from its declaration to the end of the block governed by the `for` statement, so it can be used in the termination and increment expressions as well. If the variable that controls a `for` statement is not needed outside of the loop, it's best to declare the variable in the initialization expression. The names `i`, `j`, and `k` are often used to control `for` loops; declaring them within the initialization expression limits their life span and reduces errors.

> The three expressions of the `for` loop are optional; an infinite loop can be created as follows:

> >     for ( ; ; ) {    // infinite loop

> >          // your code goes here
> >     }

> The `for` statement also has another form designed for iteration through Collections and arrays This form is sometimes referred to as the enhanced for statement, and can be used to make your loops more compact and easy to read. To demonstrate, consider the following array, which holds the numbers 1 through 10:

> >     int[] numbers = {1,2,3,4,5,6,7,8,9,10};

> The following program, `EnhancedForDemo`, uses the enhanced `for` to loop through the array:

> >     class EnhancedForDemo {
> >          public static void main(String[] args){
> >               int[] numbers = {1,2,3,4,5,6,7,8,9,10};
> >               for (int item : numbers) {
> >                 System.out.println("Count is: " + item);
> >               }
> >          }
> >     }

> In this example, the variable `item` holds the current value from the numbers array. The output from this program is the same as before:

> >     Count is: 1
> >     Count is: 2
> >     Count is: 3
> >     Count is: 4
> >     Count is: 5
> >     Count is: 6
> >     Count is: 7
> >     Count is: 8
> >     Count is: 9
> >     Count is: 10

> We recommend using this form of the `for` statement instead of the general form whenever possible.

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