What does : (colon) mean in Java Programming

In this post, we will learn about what does a colon means in Java programming. The colon operator can be used in various ways in Java as mentioned below:
1. Enhanced for loops (for-each loop)
2. Ternary expression
3. Labeling of the loops
4. Switch statements after case or default

Read Also: What does | mean in Java with examples

What does a colon mean in Java Programming

According to Oracle docs, When you see the colon(:) read it as "in". Let's dive deep into more detail:

1. Enhanced for loops (for-each loop)

The enhanced for loop was introduced in Java 5. It was mainly introduced to traverse the collection of elements including arrays. The main advantage of using for each loop is that it makes the code more readable and eliminates the possibility of bugs.

Syntax:

For-each loop syntax consists of datatype with the variable followed by a colon(:) then collection or array.

 for(dataType variable : collection | array)
{
  // statements
} 

Example:

1. Array

Suppose we have givenArray, then we can traverse it using conventional for loop or using new enhanced for loop(for-each loop) as shown below in the image:

 public class ColonJava {
    public static void main(String args[]) {
        // Declaring the Array
        int[] givenArray = {11, 7, 45, 19};
        // Traversing the array using for-each loop
        for (int val : givenArray)
        {
            System.out.println(val);
        }
    }
}

Output:
11
7
45
19

One of the downsides of the for-each loop is that you can not traverse elements in reverse order. Also, you can not skip any number of elements.

2. Ternary expression

As the name suggests, the ternary operator takes three terms and its syntax is:

Syntax:

 BooleanExpression ? Expression1 : Expression2

The value of the BooleanExpression is determined. If it is true, then the value of the whole expression is Expression1, else, if it is false then the value of the whole expression is Expression2.

Example:

 public class ColonJava2 {
    public static void main(String args[]) {
        boolean val = true;
        int x = val ? 9 : 2;
        System.out.println(x);
    }
}

Output:
9

3. Labeling of the loops

In Java, a label is a valid variable name. The label denotes the name of the loop to where the control of execution should jump. It is simple to label a loop, place the label before the loop with a colon at the end as shown below in the example:

 public class ColonJava3 {
    public static void main(String args[]) {
        int i, j=0;
        //outer label
        outerloop:
        for(i=0; i < 3; i++) {
            System.out.print(i+" ");
            // inner label
            innerloop:
            for(j=0; j < 4;j++) {
                System.out.print(j + " ");
                if (j==1)
                    break innerloop;
            }    
        }    
    }
}

Output:
0 0 1 1 0 1 2 0 1

4. Switch statements after case or default

The simple syntax of the switch statement is given below:

 switch(expression){
case a:
    // statements
    break;
case b:
    // statements
    break;
default:
    //statements
}

You can see that we have used colon(:) after the case and default keywords. You can find in detail the switch statements here.

That's all for today, please mention in the comments in case you have any questions related to what does a colon means in Java programming.