How to implement Builder Design Pattern in Java ?.

Program to demonstrate how to implement Builder Design Pattern in Java.

package com.hubberspot.designpattern.creational.builder;

// 1. Create a Robot class which is to be build by 
// Builder Design Pattern.
public class Robot {

    // 2. Robot has few properties/characteristics
    private String robotHead;
    private String robotTorso;
    private String robotArms;
    private String robotLegs;

    // 3. Create getters for each characteristics
    public String getRobotHead() {
        return robotHead;
    }

    public String getRobotTorso() {
        return robotTorso;
    }

    public String getRobotArms() {
        return robotArms;
    }

    public String getRobotLegs() {
        return robotLegs;
    }

    // 4. Create a static class which will build our 
    // Robot
    public static class RobotBuilder {
        
        // 5. Provide it with properties with which it will
        // prepare the required Robot
        private String robotHead = "";
        private String robotTorso = "" ;
        private String robotArms = "";
        private String robotLegs = "";

        public RobotBuilder() {

        }

        // 6. Create methods for each properties which Robot 
        // requires to get in action. The client will pass
        // necessary values for the type of Robot they want.
        public RobotBuilder buildRobotHead(String robotHead) {
            this.robotHead = robotHead;
            return this;
        }

        public RobotBuilder buildRobotTorso(String robotTorso) {
            this.robotTorso = robotTorso;
            return this;
        }

        public RobotBuilder buildRobotArms(String robotArms) {
            this.robotArms = robotArms;
            return this;
        }

        public RobotBuilder buildRobotLegs(String robotLegs) {
            this.robotLegs = robotLegs;
            return this;
        }

        // 7. Final build method will return us back the required 
        // Robot
        public Robot build() {
            return new Robot(this);
        }
    }

    // 8. Actual preparation of Robot by RobotBuilder
    private Robot(RobotBuilder robotBuilder) {
        robotHead = robotBuilder.robotHead;
        robotTorso = robotBuilder.robotTorso;
        robotArms = robotBuilder.robotArms;
        robotLegs = robotBuilder.robotLegs;
    }

    // 9. Creation of Iron Robot and Steel Robot by the 
    // client.
    public static void main(String[] args) {

        System.out.println("Let's build a Iron Robot .... \n");
        
        Robot ironRobot = new Robot.RobotBuilder()
              .buildRobotHead("Iron Head")
              .buildRobotTorso("Iron Torso")
              .buildRobotArms("Iron Arms")
              .buildRobotLegs("Iron Legs")
              .build();
        
        System.out.println("Iron Robot is build with following specs : \n");

        System.out.println("Robot Head : " + ironRobot.getRobotHead());
        System.out.println("Robot Torso : " + ironRobot.getRobotTorso());
        System.out.println("Robot Arms : " + ironRobot.getRobotArms());
        System.out.println("Robot Legs : " + ironRobot.getRobotLegs());
        
        System.out.println();
        
        System.out.println("Let's build a Steel Robot .... \n");
        
        Robot steelRobot = new Robot.RobotBuilder()
              .buildRobotHead("Steel Head")
              .buildRobotTorso("Steel Torso")
              .buildRobotArms("Steel Arms")
              .buildRobotLegs("Steel Legs")
              .build();
        
        System.out.println("Steel Robot is build with following specs : \n");

        System.out.println("Robot Head : " + steelRobot.getRobotHead());
        System.out.println("Robot Torso : " + steelRobot.getRobotTorso());
        System.out.println("Robot Arms : " + steelRobot.getRobotArms());
        System.out.println("Robot Legs : " + steelRobot.getRobotLegs());
              
    }
}

Output of the program :