Week 1: Types, condition clauses and loops/14a. for loops

for (<initialization>; <condition>; <change>) {

    <block>

}


==================================================



public class Example {
    public static void main(String[] args) {
        for (int i=1; i<=10; i++) {
            System.out.println(i);
        }
    }
}

Output:
1
2
3
4
5
6
7
8
9
10

    

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Components of the loop are all optional - so you can omit the initialization, condition clause or modification (or even all of them).
However, semicolons are mandatory.


public static void main(String[] args) {
        // variable initialized outside for-loop
        int i = 1;
        for (; i<=10; i++) {
            System.out.println(i);
        }

        // making the variable modification inside the loop
        for (int j = 5; j > 1;) {
            System.out.println(j);
            j--;
        }

        // eternal loop
        for(;;) {
            // this is printed until the user 
            // closes the program: in practice the same as while(true)
            System.out.println("Hi!");
        }

    }
}
 


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A change in the value of a variable in a for statement is usually done with the ++ and -- operators.
These operators increase or decrease the value of a variable by one, for example:

public class Example {
    public static void main(String[] args) {
        int a = 3;
        a++;
        System.out.println(a);

        a--;
        a--;
        System.out.println(a);

        // This first prints the value and then
        // after that increases it:
        System.out.println(a++);

        // one more print
        System.out.println(a);

    }
}

Output:
4
2
2
3