Java 8 Feature – Method References

Method References feature is included in Java 8. This feature is used whenever there is a need for calling an existing method using Lambda Expressions. Method References can be used as an alternative approach for calling such methods as this will create more readable code.

There are majorly 4 types of Method References. All kinds with their respective syntax are mentioned below –

Kinds of Method References

:: is an operator to remember

S. No.	Kind	Syntax
1	Reference to a static method	ContainingClass::staticMethodName
2	Reference to an instance method of a particular object	containingObject::instanceMethodName
3	Reference to an instance method of any arbitrary object of a particular type	ContainingType::methodName
4	Reference to a constructor	ClassName::new

Examples of Method References

Java Code with Output and explanation for each type of Method References are mentioned below –

Reference to a Static method

Below is the Java Code for “Reference to a static method”.

Java Code

package com.thinkconstructive;

import java.util.function.BiFunction;

public class MethodReferenceDemoOne {
    public static <T> T concatOperation(T one, T two, BiFunction<T, T, T> concatenateOp){
        return concatenateOp.apply(one, two);
    }

    public static String concatNames(String one, String two)
    {
        return one + two;
    }

    public static void main(String args[])
    {
        MethodReferenceDemoOne methodReferenceDemoOne = new MethodReferenceDemoOne();

        // With Lambda Expression
        System.out.println(MethodReferenceDemoOne.concatOperation(
                "Head","First",(nameOne, nameTwo) -> nameOne + nameTwo
        ));

        //Without Lambda Exp  -  With Method References
        System.out.println(MethodReferenceDemoOne.concatOperation(
                "Java","Black", MethodReferenceDemoOne::concatNames
        ));
    }
}

Output

HeadFirst
JavaBlack

Explanation

In the above code MethodReferenceDemoOne class contains a Static method named as concatNames(). This method is called in main() method with the help of Method References technique and required code gets executed.

Method Reference call is MethodReferenceDemoOne::concatNames

Reference to an instance method of a particular object

Below is the Java Code for “Reference to an instance method of a particular object”.

Java Code

package com.thinkconstructive;

import java.util.function.BiFunction;

public class MethodReferenceDemoOne {
    public static <T> T concatOperation(T one, T two, BiFunction<T, T, T> concatenateOp){
        return concatenateOp.apply(one, two);
    }

    public String concatNamesForInstance(String one, String two)
    {
        return one + two;
    }

    public static void main(String args[])
    {
        MethodReferenceDemoOne methodReferenceDemoOne = new MethodReferenceDemoOne();

        // With Lambda Expression
        System.out.println(MethodReferenceDemoOne.concatOperation(
                "Head","First",(nameOne, nameTwo) -> nameOne + nameTwo
        ));

        //Without Lambda Exp  - With Method References - Instance Method
        System.out.println(MethodReferenceDemoOne.concatOperation(
                "Oracle", "Java",methodReferenceDemoOne::concatNamesForInstance
        ));

        //Without Lambda Exp  - With Method References -

    }
}

Output

HeadFirst
OracleJava

Explanation

In the above code MethodReferenceDemoOne class contains an Instance method named as concatNamesForInstance(). This method is called in main() method with the help of Method References technique and required code gets executed.

Method Reference call is methodReferenceDemoOne::concatNamesForInstance

Reference to a Constructor

Below is the Java code for “Reference to Constructor”

Java Code

package com.thinkconstructive;

@FunctionalInterface
interface MRDemoInterface{
    MRDemo printMsg(String msg);
}

class MRDemo{
    public MRDemo(String msg)
    {
        System.out.println(msg);
    }
}

public class MethodReferenceDemoTwo {
    public static void main(String args[])
    {
        // Reference to a Constructor
        MRDemoInterface mrDemoInterface = MRDemo::new;
        mrDemoInterface.printMsg("Java Champion");
    }
}

Output

Java Champion

Explanation

In the above code MRDemo class contains its Constructor. This class’s Constructor is called in main() method with the help of Method References technique and required code gets executed.

Method Reference call is MRDemo::new

Code Repository

Java Code Example of Method Reference is available HERE

Video Tutorial

Video Tutorial of Method Reference is available HERE