Java provides several mechanisms to implement abstraction effectively:

1. Abstract Classes:
An abstract class in Java serves as a blueprint for other classes and cannot be instantiated itself. It often contains abstract methods, which are declared but not implemented within the abstract class. Subclasses that inherit from an abstract class must provide implementations for these abstract methods. Abstract classes can also include concrete methods, providing default behavior for subclasses.

Example of an abstract class:

abstract class Shape {
// Abstract method (no implementation)
public abstract double area();
}

class Rectangle extends Shape {
private double width;
private double height;

public Rectangle(double width, double height) {
this.width = width;
this.height = height;
}

// Implementing abstract method
@Override
public double area() {
return width * height;
}
}

2. Interfaces:
Interfaces in Java define a contract for classes to follow. They consist of method signatures without implementations. Classes that implement an interface must provide concrete implementations for all the methods declared in the interface. Unlike abstract classes, a class can implement multiple interfaces, enabling a form of multiple inheritance in Java.

Example of an interface:

interface Animal {
void eat();
void sleep();
}

class Dog implements Animal {
@Override
public void eat() {
System.out.println("Dog is eating.");
}

@Override
public void sleep() {
System.out.println("Dog is sleeping.");
}
}