KEYWORDS - JAVA PROGRAMMING

Keywords in Java Programming Java programming is a popular and versatile language used for developing a wide range of applications. To truly understand Java, it's essential to grasp the fundamental keywords that form the building blocks of the language. In this article, we will explore and explain the most important keywords in Java, from import to long, providing clear examples and explanations for beginners to advance their understanding.

1. Import

The import keyword is used to include external classes or packages in your Java program. It allows you to access classes, methods, and variables from other packages. For instance, if you want to use the Scanner class from the java.util package to take user input, you would write:

Code :

import java.util.Scanner;

This allows you to use the Scanner class without typing its full package name every time.

2. Class

The class keyword is used to define a blueprint for creating objects. It encapsulates data and methods that operate on that data.

For example:

Code :

public class Student { String name; int age; void displayInfo() { System.out.println("Name: " + name + ", Age: " + age); } }

Read more : OOPS CONCEPTS - JAVA PROGRAMMING

3. This

The this keyword refers to the current instance of a class. It's used to distinguish between instance variables and parameters with the same name. For instance:

Code :

public class Circle { double radius; Circle(double radius) { this.radius = radius; // Assigning parameter value to instance variable } }

4. Super

The super keyword is used to access methods and variables from a parent class. It's often used in inheritance scenarios. Consider:

Code :

class Parent { void show() { System.out.println("This is the parent class."); } } class Child extends Parent { void display() { super.show(); // Calling parent class method } }

5. Extends

The extends keyword is used to create a subclass that inherits properties and behaviors from a superclass. For instance:

Code :

class Animal { void makeSound() { System.out.println("Some sound"); } } class Dog extends Animal { void makeSound() { System.out.println("Bark!"); } }

6. Package

The package keyword is used to define the package name for your Java class. It helps organize and categorize classes into meaningful groups.

For example:

Code :

package com.example.myapp;

public class MyClass { // Class content }

7. Return

The return keyword is used within a method to send a value back to the caller. It exits the method and can be used to pass a result. Here's an example:

Code :

public int add(int a, int b) { return a + b; }

8. Try, Catch, Finally

The trio of try, catch, and finally is used for exception handling. The try block contains the code that might raise an exception, the catch block handles the exception, and the finally block is executed regardless of whether an exception occurred or not.

Code :

try { // Code that might throw an exception } catch (Exception e) { // Handle the exception } finally { // Code to be executed regardless of exception }

9. Throw and Throws

The throw keyword is used to manually throw an exception in your code. The throws keyword is used in method signatures to indicate that a method might throw a certain type of exception.

Code :

void myMethod(int x) throws CustomException { if (x < 0) { throw new CustomException("Negative value not allowed"); } }

10. Final

The final keyword is used to declare that a variable, method, or class cannot be modified or extended. For instance:

Code :

final int myConstant = 10;

11. Public, Private, Protected

These access modifiers control the visibility of classes, methods, and variables in Java. Public makes them accessible everywhere, private restricts access to the same class, and protected allows access within the same package and subclasses.

Code :

public class MyClass { private int secretNumber; protected String myString; }

12. Static

The static keyword is used to declare methods and variables as class-level instead of instance-level. This means they are shared among all instances of the class. For instance:

Code :

public class Counter { static int count = 0; Counter() { count++; } }

13. Instance Of

The instanceof keyword is used to check if an object belongs to a particular class or interface. It's often used for type checking before casting objects.

Code :

if (myObject instanceof Dog) { Dog dog = (Dog) myObject; // Safely cast to Dog }

14. Enum

The enum keyword is used to define a type with a fixed set of constants. It's commonly used to represent categories, states, or options.

Code :

enum Days { MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY }

15. Interface

The interface keyword is used to define a contract for classes to implement. It only contains method signatures. A class can implement multiple interfaces.

Code :

interface Shape { double area(); double perimeter(); } class Circle implements Shape { // Implement area() and perimeter() methods }

16. Assert

The assert keyword is used to perform debugging checks in your code. If the given condition is false, it throws an AssertionError.

Code :

int age = -1; assert age >= 0 : "Age cannot be negative";

17. Native

The native keyword is used to indicate that a method is implemented in native code, typically written in another language like C or C++.

Code :

public native void myNativeMethod();

18. Volatile

The volatile keyword is used to declare a variable as volatile, which means it's subject to changes from multiple threads. It ensures that the latest value is always read.

Code :

volatile boolean flag = false;

19. Implements

The implements keyword is used to indicate that a class is implementing an interface. It ensures that the class provides implementations for all the methods defined in the interface.

Code :

class MyCalculator implements Calculator { // Implement methods from Calculator interface }

20. Abstract

The abstract keyword is used to declare a class or method as abstract, meaning it cannot be instantiated directly or must be overridden by a subclass.

Code :

abstract class Shape { abstract double area(); } class Circle extends Shape { // Override area() method }

21. Do, While

The do-while loop is used to execute a block of code at least once before checking the loop condition. For example:

Code :

int i = 0; do { System.out.println(i); i++; } while (i < 5);

22. For, While

The for and while loops are used for repetitive execution of a block of code based on a condition.

Code :

for (int i = 0; i < 5; i++) { System.out.println(i); } int j = 0; while (j < 5) { System.out.println(j); j++; }

23. If, Else

The if and else keywords are used for conditional branching in Java. They allow you to execute different code blocks based on the evaluation of a condition.

Code :

int age = 18; if (age >= 18) { System.out.println("You are an adult"); } else { System.out.println("You are a minor"); }

24. Switch, Case, Default

The switch statement is used to evaluate an expression against multiple possible values. Each possible value is associated with a case label. The default label is executed if none of the cases match.

Code :

int day = 3; switch (day) { case 1: System.out.println("Monday"); break; case 2: System.out.println("Tuesday"); break; default: System.out.println("Other day"); }

25. Break, Continue

The break keyword is used to exit loops or switch statements prematurely. The continue keyword is used to skip the rest of the loop iteration and move to the next iteration.

Code :

for (int i = 0; i < 10; i++) { if (i == 5) { break; // Exit the loop when i is 5 } System.out.println(i); } for (int j = 0; j < 10; j++) { if (j % 2 == 0) { continue; // Skip even numbers } System.out.println(j); }

26. Primitive Data Types

Java has several primitive data types, including boolean, byte, short, int, char, float, double, and long. These types store simple values.

Code :
int age = 25; char grade = 'A'; double salary = 50000.0; boolean isActive = true;

Conclusion

In this comprehensive guide, we've delved into the most essential keywords in Java programming. These keywords form the foundation of the language, enabling developers to create powerful and robust applications. From managing exceptions with try-catch-finally to controlling access with public-private-protected, and from looping with for-while-do to making decisions with if-else-switch, these keywords shape the flow and structure of your Java programs. By understanding and mastering these keywords, you'll be well on your way to becoming a proficient Java programmer.