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 | () -> “w3schools”.toString() |
| Reference to a constructor | String::new | () -> new String() |
Method reference to a static method of a class
package com.w3schools;
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
Thread is running...
Method reference to an instance method of an object
package com.w3schools;
@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
Hello Jai
Method reference to a constructor
package com.w3schools;
@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 w3schools");
}
}
Output
Hello w3schools