Java Modifiers

In Java, modifiers are keywords that are used to modify the behavior of classes, methods, variables, and other program elements. There are several types of modifiers in Java, each with its own purpose.

Here’s a brief overview of some of the most common modifiers in Java:

Access Modifiers: These modifiers determine the accessibility of classes, methods, and variables from different parts of a Java program. There are four access modifiers in Java: public, protected, private, and the default (no modifier).
Non-access Modifiers: These modifiers do not affect the accessibility of program elements, but modify their behavior in other ways. Some examples of non-access modifiers in Java include static, final, abstract, synchronized, transient, and volatile.
Class Modifiers: These modifiers are used to modify the behavior of classes. Some examples of class modifiers in Java include abstract, final, and strictfp.
Method Modifiers: These modifiers are used to modify the behavior of methods. Some examples of method modifiers in Java include abstract, final, synchronized, and static.
Variable Modifiers: These modifiers are used to modify the behavior of variables. Some examples of variable modifiers in Java include final, static, volatile, and transient.

Access Modifiers

In Java, access modifiers are used to control the visibility of classes, methods, and variables from different parts of a program. There are four access modifiers in Java: public, protected, private, and the default (no modifier). Here’s a brief overview of each access modifier and how they work:

public: This is the most permissive access modifier, allowing classes, methods, and variables to be accessed from anywhere in a program. Here’s an example:
```
public class Person {
    public String name; // public variable

    public void sayHello() { // public method
        System.out.println("Hello!");
    }
}
```
In this example, the name variable and sayHello() method are both public, which means they can be accessed from any part of the program.
private: This access modifier restricts access to classes, methods, and variables to the same class in which they are declared. Here’s an example:
```
public class Person {
    private String name; // private variable

    private void sayHello() { // private method
        System.out.println("Hello!");
    }
}
```
In this example, the name variable and sayHello() method are both private, which means they can only be accessed from within the Person class.
protected: This access modifier allows classes, methods, and variables to be accessed within the same package or by subclasses in different packages. Here’s an example:
```
package com.example;

public class Person {
    protected String name; // protected variable

    protected void sayHello() { // protected method
        System.out.println("Hello!");
    }
}
```
In this example, the name variable and sayHello() method are both protected, which means they can be accessed from within the Person class, any subclass of Person, and any class in the same package as Person.
Default (no modifier): A member with no access modifier (also called “package-private”) can be accessed from within the same package. For example:
```
package com.example;

public class Person {
    String name; // default (package-private) variable

    void sayHello() { // default (package-private) method
        System.out.println("Hello!");
    }
}
```
In this example, the name variable and sayHello() method have no access modifier, which means they can only be accessed from within the Person class and any other class in the same package as Person.

Access modifiers are an important part of Java programming, as they allow you to control the visibility and accessibility of different program elements.

Non-access Modifiers:

In Java, non-access modifiers are used to modify the behavior of classes, methods, variables, and other program elements. Non-access modifiers do not affect the accessibility of program elements, but rather modify their behavior in other ways.

Here are some of the most common non-access modifiers in Java:

static: A static member (variable or method) belongs to the class itself, rather than to any specific object of the class. This means that you can access a static member without creating an object of the class. For example:
```
public class MathUtils {
    public static int add(int a, int b) { // static method
        return a + b;
    }

    public static final double PI = 3.14159265; // static final variable
}
```
In this example, the add() method and PI variable are both static, which means they belong to the MathUtils class itself rather than any specific object of the class.
final: A final member (variable or method) cannot be changed once it has been initialized. For example:
```
public class Person {
    private final String name; // final variable

    public Person(String name) {
        this.name = name;
    }

    public final void sayHello() { // final method
        System.out.println("Hello, my name is " + name);
    }
}
```
In this example, the name variable is final, which means it cannot be changed once it has been initialized in the constructor. The sayHello() method is also final, which means it cannot be overridden by subclasses.
abstract: An abstract class or method is one that cannot be instantiated directly, but must be subclassed and implemented. For example:
```
public abstract class Shape {
    public abstract double getArea(); // abstract method
}

public class Circle extends Shape {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

    public double getArea() { // implementation of abstract method
        return Math.PI * radius * radius;
    }
}
```
In this example, the Shape class is abstract, which means it cannot be instantiated directly, but must be subclassed and implemented. The getArea() method is also abstract, which means it must be implemented by any subclass of Shape.
synchronized: A synchronized method is one that can only be accessed by one thread at a time, to prevent concurrent access to shared resources. For example:
```
public class Counter {
    private int count;

    public synchronized void increment() { // synchronized method
        count++;
    }

    public synchronized void decrement() { // synchronized method
        count--;
    }
}
```
In this example, the increment() and decrement() methods are both synchronized, which means that only one thread can access them at a time, to prevent concurrent access to the count variable.

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