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Java Loops Examples

by Didin J. on Mar 14, 2023 Java Loops Examples

The collection of Java Loops through Array, List, and Collection examples with source codes

Looping is a fundamental and essential feature in every Programming Language including Java. Loops a control flow statement for traversing or iterating items in a collection, array, list, set, etc. There are a lot of ways to loop through collection, array, list, or set in Java. It can use classic for, do-while, while, or for-in. This time, we will show you examples that are used in real Java applications or projects.

Table of Contents:

Before jumping to the example, make sure you have installed Java Virtual Machine and the Java Development Kit (JDK). You can download and install it from Oracle https://www.oracle.com/java/technologies/downloads/ or OpenJDK https://openjdk.org/projects/jdk/19/. Then set the JAVA_HOME or java and javac commands to the environment variable. After Java setup and can run correctly then open your IDE or Text Editor. We are using VSCode, so, in the Java apps folder we just type this command.

cd JavaApps
code .

To check the installed java version, type these commands in the terminal or cmd.

java -version
java version "19.0.2" 2023-01-17
Java(TM) SE Runtime Environment (build 19.0.2+7-44)
Java HotSpot(TM) 64-Bit Server VM (build 19.0.2+7-44, mixed mode, sharing)

javac -version
javac 19.0.2

Now, in the VSCode, create a new Java file JavaLoopsExample.java. We will put all examples for this tutorial in this file.


For Loop Examples

The first example will be running inside the main method that will execute first. For that add these lines of codes in the file JavaLoopsExample.java.

public class JavaLoopsExample {
    public static void main(String[] args) {
    
    }
}

The classical looping thought the collection, array, list, or set in Java or C is the "for" keyword.

Classic For Loop example:

        String[] animals = { "Lion", "Elephant", "Fox", "Eagle" };

        for (int i = 0; i < animals.length; i++) {
            System.out.println(animals[i]);
        }

Results:

Lion
Elephant
Fox
Eagle

For loop with comma-separated expressions example:

        for (int i = 1, j = 10; i < j; i++, j--) {
            System.out.println(i + ", " + j);
        }

Results:

1, 10
2, 9
3, 8
4, 7
5, 6

For loop multi variables example:

        for (int x = 0, y = 10, z = 1; z < y; z++)
            System.out.println("X: " + x + ",Y: "+ y + ", Z: " + z);


Results:

X: 0,Y: 10, Z: 2
X: 0,Y: 10, Z: 3
X: 0,Y: 10, Z: 4
X: 0,Y: 10, Z: 5
X: 0,Y: 10, Z: 6
X: 0,Y: 10, Z: 7
X: 0,Y: 10, Z: 8
X: 0,Y: 10, Z: 9

The multiple variables in this example should be the same type.


For In-Loop Examples

Iterate over a list of objects example:

import java.util.ArrayList;
import java.util.List;

class JavaLoopsExample {
    static class Framework {
        String name;
        String type;
        int gitStars;
    }

    public static void main(String[] args) {
        List<Framework> frameworks = new ArrayList<>();
        Framework framework1 = new Framework();
        framework1.name = "Spring";
        framework1.type = "Java";
        framework1.gitStars = 32000;
        frameworks.add(framework1);
        Framework framework2 = new Framework();
        framework2.name = "Flask";
        framework2.type = "Python";
        framework2.gitStars = 10000;
        frameworks.add(framework2);
        Framework framework3 = new Framework();
        framework3.name = "Quarkus";
        framework3.type = "Java";
        framework3.gitStars = 50000;
        frameworks.add(framework3);

        for (Framework framework: frameworks) {
            System.out.println(framework.name + " (" + framework.type + ") -> " + framework.gitStars);
        }
    }
}

Results:

Spring (Java) -> 32000
Flask (Python) -> 10000
Quarkus (Java) -> 50000

Iterate over an array of string examples:

        String[] carNameArray = { "BMW", "Mercedez Benz", "Volvo" };

        for (String car: carNameArray) {
            System.out.println(car);
        }

Results:

BMW
Mercedez Benz
Volvo

Iterate over map example:

import java.util.HashMap;
import java.util.Map;

class JavaLoopsExample {

    public static void main(String[] args) {

        Map<String, Integer> cars = new HashMap<>();
        cars.put("BMW", 45000);
        cars.put("Mercedez Benz", 44000);
        cars.put("Volvo", 30000);

        for (Map.Entry<String, Integer> car :
             cars.entrySet()) {
            System.out.print(car.getKey() + ":");
            System.out.println(car.getValue());
        }
    }
}

Results:

Volvo:30000
Mercedez Benz:44000
BMW:45000


Infinite Loop Examples

The basic loop without any variable and assignment will be an infinite loop.

Infinite loop example using for:

import java.util.Date;

class JavaLoopsExample {

    public static void main(String[] args) {
        for(;;) {
            System.out.println(new Date());
        }
    }
}

Results:

Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
...

Press CTRL+C to stop the infinite loop.

Infinite loop example using do-while:

        do {
            System.out.println(new Date());
        } while (true);

Results:

Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
...

Press CTRL+C to stop the infinite loop.

Infinite loop example using while:

        while (true) {
            System.out.println(new Date());
        }

Results:

Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
Tue Mar 14 16:00:14 WIB 2023
...


While Loop Examples

Iterate over an array of strings using classic while example:

        String[] cars = { "BMW", "Mercedez Benz", "Volvo" };
        int x = 0;

        while ( x < cars.length ) {
            System.out.println(cars[x]);
            x++;
        }

Result:

BMW
Mercedez Benz
Volvo


Do/While Loop Examples

Classic Java-style do/while example:

        String[] cars = { "BMW", "Mercedez Benz", "Volvo" };
        int x = 0;

        do {
            System.out.println(cars[x]);
            x++;
        } while(cars.length > x);

Results:

BMW
Mercedez Benz
Volvo


Nested Loop Examples

A nested loop is a loop inside a loop or a loop has a child loop.

Nested loop example to print simple pyramid:

        int x, y;

        // parent loop
        for(x = 0; x < 7; x++) { 
            // child loop
            for(y = 0; y <= x; y++)
            {
                System.out.print("* ");
            }
            System.out.println();
        }

Results:

* 
* *
* * *
* * * *
* * * * *
* * * * * *
* * * * * * *

Nested loop example to print triangle:

        for (int x = 0; x < 7; x++) {
            for (int y = 7 - x; y > 1; y--)
            {
                System.out.print(" ");
            }

            for (int y = 0; y <= x; y++ )
            {
                System.out.print("* ");
            }
   
            System.out.println();
        }

Results:

      * 
     * *
    * * *
   * * * *
  * * * * *
 * * * * * *
* * * * * * *

That it's, an example of Java loops. We are wrapping the examples in one file in GitHub.

That just the basic. If you need more deep learning about Java and Spring Framework you can take the following cheap course:

Thanks!

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