Abstract Keyword In Java Code Example

Example 1: abstract class in java

Sometimes we may come across a situation where we cannot provide  implementation to all the methods in a class. We want to leave the  implementation to a class that extends it. In such case we declare a class as abstract.To make a class abstract we use key word abstract.  Any class that contains one or more abstract methods is declared as abstract.  If we don’t declare class as abstract which contains abstract methods we get  compile time error.      1)Abstract classes cannot be instantiated   2)An abstarct classes contains abstract method, concrete methods or both.   3)Any class which extends abstarct class must override all methods of abstract     class   4)An abstarct class can contain either 0 or more abstract method.

Example 2: What are abstract methods in java

An abstract method is the method which does’nt have any body.  Abstract method is declared with keyword abstract and semicolon in place of method body.    public abstract void <method name>(); Ex : public abstract void getDetails(); It is the responsibility of subclass to provide implementation to  abstract method defined in abstract class

Example 3: how to make abstract method in java

public abstract class Account {		//abstract class //perent class     protected int accountNumber;     protected Customer customerObj;     protected double balance;   	//constructor   	public Account(int saccountNumber, Customer scustomerObj,double sbalance){         accountNumber = saccountNumber;         customerObj = scustomerObj;         balance = sbalance;     }   	// abstract Function     public abstract boolean withdraw(double amount);  }     public class SavingsAccount extends Account { // child class     private double minimumBalance;   	// constructor     public SavingsAccount(int saccountNumber, Customer scustomerObj, double sbalance, double sminimumBalance) {         super(saccountNumber, scustomerObj, sbalance);         minimumBalance = sminimumBalance;     } 	// Implementation of abstract function in child class     public boolean withdraw(double amount) {         if (balance() > minimumBalance && balance() - amount > minimumBalance) {             super.setBalance(balance() - amount);             return true;         } else {             return false;         }     } }

Example 4: java abstract class

// abstract class abstract class Shape {    // abstract method    abstract void sides(); } class Triangle extends Shape {    void sides()    {       System.out.println("Triangle shape has three sides.");    } } class Pentagon extends Shape {    void sides()    {       System.out.println("Pentagon shape has five sides.");    }    public static void main(String[] args)    {       Triangle obj1 = new Triangle();       obj1.sides();       Pentagon obj2 = new Pentagon();       obj2.sides();    } }

Example 5: abstract class in java

public abstract class GraphicObject {     abstract void draw(); }

Example 6: how to create an abstract method in java

abstract class Scratch{   // cannot be static     abstract public void hello();     abstract String randNum(); }  interface Other{   //all methods in an interface are abstract     public void bye();     String randDouble(); }