Check out example codes for "abstraction in java". It will help you in understanding the concepts better.

Code Example 1

Abstraction is nothing but the quality of dealing with ideas rather than 
events. It basically deals with hiding the internal details and showing 
the essential things to the user.

Code Example 2

public abstract class GraphicObject {

   abstract void draw();

Code Example 3

Abstraction is defined as hiding internal implementation and showing only 
necessary information.
// abstract class
abstract class Addition
   // abstract methods
   public abstract int addTwoNumbers(int number1, int number2);
   public abstract int addFourNumbers(int number1, int number2, int number3, int number4);
   // non-abstract method
   public void printValues()
      System.out.println("abstract class printValues() method");
class AbstractMethodExample extends Addition
   public int addTwoNumbers(int number1, int number2)
      return number1 + number2;
   public int addFourNumbers(int number1, int number2, int number3, int number4)
      return number1 + number2 + number3 + number4;
   public static void main(String[] args)
      Addition add = new AbstractMethodExample();
      System.out.println(add.addTwoNumbers(6, 6));
      System.out.println(add.addFourNumbers(8, 8, 3, 2));

Code Example 4

public class ReplaceAllExample{  
public static void main(String args[]){  
String s1="Google is a very good website";  
String replaceString=s1.replaceAll("a","e");//replaces all occurrences of "a" to "e"  

Code Example 5

Math.pow(base, esponente)

Code Example 6

public <t>

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