Strategy Pattern

Motivation

Intent

• Algorithms 들만 모아서 그룹을 만들어 상호 변경 가능하도록 구현하자

Implementation

• Strategy - 모든 구체전략에 대한 인터페이스를 제공한다.

• ConcreteStrategy - 구체 전략

• Context
• 구체 전략에대한 참조를 전략 인터페이스에 담아 보관하고 있음
• 클라이언트의 요청이 들어올 시 실질적인 알고리즘의 실행은 구체 전략에 위임

Applicablity & Examples

public interface IBehaviour {
	public int moveCommand();
}

public class AgressiveBehaviour implements IBehaviour{
	public int moveCommand()
	{
		System.out.println("\tAgressive Behaviour: if find another robot attack it");
		return 1;
	}
}

public class DefensiveBehaviour implements IBehaviour{
	public int moveCommand()
	{
		System.out.println("\tDefensive Behaviour: if find another robot run from it");
		return -1;
	}
}

public class NormalBehaviour implements IBehaviour{
	public int moveCommand()
	{
		System.out.println("\tNormal Behaviour: if find another robot ignore it");
		return 0;
	}
}

public class Robot {
	IBehaviour behaviour;
	String name;

	public Robot(String name)
	{
		this.name = name;
	}

	public void setBehaviour(IBehaviour behaviour)
	{
		this.behaviour = behaviour;
	}

	public IBehaviour getBehaviour()
	{
		return behaviour;
	}

	public void move()
	{
		System.out.println(this.name + ": Based on current position" +
					 "the behaviour object decide the next move:");
		int command = behaviour.moveCommand();
		// ... send the command to mechanisms
		System.out.println("\tThe result returned by behaviour object " +
					"is sent to the movement mechanisms " +
					" for the robot '"  + this.name + "'");
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}


public class Main {

	public static void main(String[] args) {

		Robot r1 = new Robot("Big Robot");
		Robot r2 = new Robot("George v.2.1");
		Robot r3 = new Robot("R2");

		r1.setBehaviour(new AgressiveBehaviour());
		r2.setBehaviour(new DefensiveBehaviour());
		r3.setBehaviour(new NormalBehaviour());

		r1.move();
		r2.move();
		r3.move();

		System.out.println("\r\nNew behaviours: " +
				"\r\n\t'Big Robot' gets really scared" +
				"\r\n\t, 'George v.2.1' becomes really mad because" +
				"it's always attacked by other robots" +
				"\r\n\t and R2 keeps its calm\r\n");

		r1.setBehaviour(new DefensiveBehaviour());
		r2.setBehaviour(new AgressiveBehaviour());

		r1.move();
		r2.move();
		r3.move();
	}
}

Specific problems & Implementation