- Lambda Expression Example

This section provides a tutorial example on using an lambda expression to define a class anonymously implementing a single abstract method interface. An anonymous class and a local class are used as comparisons.

My first lambda expression program,, follows an example given in a Oracle Java tutorial. Here is the source code:

 - Copyright (c) 2014,, All Rights Reserved.
class LambdaCalculator {
   interface Operation {
      int operate(int a, int b);   
   public int calculate(int a, int b, Operation o) {
      return o.operate(a, b);

   public static void main(String[] arg) {
      int x = 1;
      String s = "+";
      int y = 2;
      if (arg.length>0) x = Integer.parseInt(arg[0]);
      if (arg.length>1) s = arg[1];
      if (arg.length>2) y = Integer.parseInt(arg[2]);

      // Using a lambda expression
      Operation add = (int a, int b) -> {return a+b;};
      // Using anonymous class
      Operation subtract = new Operation() { 
      	 public int operate(int a, int b) {return a-b;} 
      // Using a local class
      class Multiply implements Operation {
      	 public int operate(int a, int b) {return a*b;} 
      Operation multiply = new Multiply();

      LambdaCalculator c = new LambdaCalculator();
      if (s.equals("+")) 
         System.out.println(x+s+y+" = "+c.calculate(x,y,add));
      else if (s.equals("-")) 
         System.out.println(x+s+y+" = "+c.calculate(x,y,subtract));
      else if (s.equals("*")) 
         System.out.println(x+s+y+" = "+c.calculate(x,y,multiply));
         System.out.println(x+s+y+" = Undefined");

Note that my sample program uses an lambda expression, an anonymous class and a local class to implement the same interface:

Now compile and run with JDK 1.8, you will get:

C:\herong>java LambdaCalculator
1+2 = 3

C:\herong>java LambdaCalculator 8 + 2
8+2 = 10

C:\herong>java LambdaCalculator 8 - 2
8-2 = 6

C:\herong>java LambdaCalculator 8 "*" 2
8*2 = 16

Here is what I learned from the output:

If we look at class files generated by the compiler, we will see only 4 of them. Any there is no class file for the "LambdaCalculator$$Lambda$1/518248" class defined by the lambda expression.

C:\herong>dir LambdaCalculator*.*

2,076 LambdaCalculator.class           - Main application class 
  214 LambdaCalculator$Operation.class - Nested interface "Operation"
  440 LambdaCalculator$1.class         - Anonymous class for "subtract
  459 LambdaCalculator$1Multiply.class - Local class "Multiply"

Last update: 2014.

Table of Contents

 About This Book

 Installing JDK 1.8 on Windows

 Execution Process, Entry Point, Input and Output

 Primitive Data Types and Literals

 Bits, Bytes, Bitwise and Shift Operations

 Managing Bit Strings in Byte Arrays

 Reference Data Types and Variables

 StringBuffer - The String Buffer Class

 System Properties and Runtime Object Methods

 Generic Classes and Parameterized Types

 Generic Methods and Type Inference

Lambda Expressions and Method References

 What Is Lambda Expression? - Lambda Expression Example

 Lambda Expression Syntax Options

 Lambda Expression as Method Reference

 Method Reference Example -

 Lambda Expression Stream Pipeline Operations

 Execution Threads and Multi-Threading Java Programs

 ThreadGroup Class and "system" ThreadGroup Tree

 Synchronization Technique and Synchronized Code Blocks

 Deadlock Condition Example Programs

 Garbage Collection and the gc() Method

 Outdated Tutorials


 PDF Printing Version