Java 8 features ,Default Methods and Static Methods

 Java as an Object oriented programming language was invented in the early 90s.

In year 2005 , added major changes such as :

1.Enhanced for loops

2.Generics

3.Type-safe enumerations.

4.Annotations.

again after 10 years , in 2015 java 8 was introduced with lot of new features :

such as :

1.Lambda Expressions

2.Method References

3.Default methods

4.New Stream API

5.New Date/Time API

6.Nashorn

-> now in java 8 ,interface introduced with some new changes.

interface can now define static methods.

interface can now define default methods.

package com.suv.java8;
public class Java8Demo implements Calculator {
	public static void main(String[] args) {
		System.out.println("Welcome to https://www.crtr4u.com/");
		Java8Demo jd = new Java8Demo();
		jd.msgDisplay();
		Calculator.sayHi();
	}
}
interface Calculator {
	default void msgDisplay() {
		System.out.println("this is default method introduced in java 8 interface");
	}
	static void sayHi() {
		System.out.println("Hi, this is static method allowed in interface from java 8");
	}
}

Output
Welcome to https://www.crtr4u.com/
this is default method introduced in java 8 interface
Hi, this is static method allowed in interface from java 8

-One Problem we must understand regarding default method in java 8 :

In Java , Multiple inheritance is not possible using classes

for example : class A extends B,C {} is not allowed in java 

But , we can implement multiple interface

for example : class A implements InterfaceB , InterfaceC{}

Now problem is , what if both interface contain default method with same signature , look at below snapshot :

As shown , In above snapshot our both interfaces contain same method with same signature , now when AClass is implementing both interface InterfaceB and InterfaceC , 

we are getting error as :

Duplicate default methods named displayMsg with the parameters () and () are inherited from the types InterfaceC and InterfaceB

we can resolve above error as :

Way 1 : Overriding default method implementing class 

Way 2 : Invoke the default method test from parent interface

-forEach() method in java 8: 

For handling Collections in better way ,forEach method is introduced ,

forEach() is the default method of Iterable interface of java.lang package.

Example : 

class Employee{
	int empId;
	String empName;
	public Employee(int empId, String empName) {
		super();
		this.empId = empId;
		this.empName = empName;
	}
	@Override
	public String toString() {
		return "Employee [empId=" + empId + ", empName=" + empName + "]";
	}	
}
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class ForEachDemo {
 public static void main(String[] args) {
	List<Employee> empList=new ArrayList<Employee>();
	empList.addAll(Arrays.asList(			
		new Employee(1,"Neel"),
		new Employee(2,"Prashant"),
                new Employee(3,"Jay"),
		new Employee(4,"Jeet"),
                new Employee(5,"RK")
	));
	empList.forEach(e->System.out.println(e));
	}
}

Output :
Employee [empId=1, empName=Neel]
Employee [empId=2, empName=Prashant]
Employee [empId=3, empName=Jay]
Employee [empId=4, empName=Jeet]
Employee [empId=5, empName=RK]

Happy Learning,thanks for reading our article.