Java 8 introduced a new feature “Method Reference” which is used to refer the methods of functional interfaces. It is a shorthand notation of a lambda expression to call a method. We can replace lambda expression with method reference (:: operator) to separate the class or object from the method name.
Types of method references
| Type |
Syntax |
Example |
| Reference to a static method |
Class::staticMethodName |
String::valueOf |
| Reference to an instance method |
object::instanceMethodName |
x::toString |
| Reference to a constructor |
ClassName::new |
String::new |
Lambda expression and Method references:
| Type |
As Method Reference |
As Lambda |
| Reference to a static method |
String::valueOf |
(s) -> String.valueOf(s) |
| Reference to an instance method |
x::toString |
() -> “w3spoint”.toString() |
| Reference to a constructor |
String::new |
() -> new String() |
Method reference to a static method of a class
package com.w3spoint;
public class MethodReference {
public static void ThreadStatus(){
System.out.println("Thread is running...");
}
public static void main(String[] args) {
Thread t2=new Thread(MethodReference::ThreadStatus);
t2.start();
}
} |
package com.w3spoint;
public class MethodReference {
public static void ThreadStatus(){
System.out.println("Thread is running...");
}
public static void main(String[] args) {
Thread t2=new Thread(MethodReference::ThreadStatus);
t2.start();
}
}
Output
Method reference to an instance method of an object
package com.w3spoint;
@FunctionalInterface
interface DisplayInterface{
void display();
}
public class MethodReference {
public void sayHello(){
System.out.println("Hello Jai");
}
public static void main(String args[]){
MethodReference methodReference = new MethodReference();
// Method reference using the object of the class
DisplayInterface displayInterface = methodReference::sayHello;
// Calling the method of functional interface
displayInterface.display();
}
} |
package com.w3spoint;
@FunctionalInterface
interface DisplayInterface{
void display();
}
public class MethodReference {
public void sayHello(){
System.out.println("Hello Jai");
}
public static void main(String args[]){
MethodReference methodReference = new MethodReference();
// Method reference using the object of the class
DisplayInterface displayInterface = methodReference::sayHello;
// Calling the method of functional interface
displayInterface.display();
}
}
Output
Method reference to a constructor
package com.w3spoint;
@FunctionalInterface
interface DisplayInterface{
Hello display(String say);
}
class Hello{
public Hello(String say){
System.out.print(say);
}
}
public class MethodReference {
public static void main(String[] args) {
//Method reference to a constructor
DisplayInterface ref = Hello::new;
ref.display("Hello w3spoint");
}
} |
package com.w3spoint;
@FunctionalInterface
interface DisplayInterface{
Hello display(String say);
}
class Hello{
public Hello(String say){
System.out.print(say);
}
}
public class MethodReference {
public static void main(String[] args) {
//Method reference to a constructor
DisplayInterface ref = Hello::new;
ref.display("Hello w3spoint");
}
}
Output