1.分析專案中變化部分與不變部分

2.多用組合，少用繼承；用行為類組合，而不是行為的繼承

案例：

第一步，把行為抽象為介面

package top.littlepage.designPattern.Strategy;

public interface FlyBehavior {
    void fly();
}

第二步，把具體行為用實體類實現

package top.littlepage.designPattern.Strategy;

public class BadFly implements FlyBehavior{

    @Override
    
 
public void fly() {
        System.out.println("--bad fly--");
    }
    
}

package top.littlepage.designPattern.Strategy;

public class NotFly implements FlyBehavior{

    @Override
    public void fly() {
        System.out.println("--not fly--");
    }

}

package top.littlepage.designPattern.Strategy;

 
public class GoodFly implements FlyBehavior{

    @Override
    public void fly() {
        System.out.println("--good fly--");
    }

}

第三步，做出具體的環境進行實現該實體

package top.littlepage.designPattern.Strategy;

public class Bird {
    private String name;
    private int age;
    private GoodFly goodfly;
    
 
private BadFly badfly;
    private NotFly notfly;
    
    public Bird() {
        name="";
        age=0;
        goodfly=new GoodFly();
        badfly=new BadFly();
        notfly=new NotFly();
    }
    public GoodFly getGoodfly() {
        return goodfly;
    }
    public void setGoodfly(GoodFly goodfly) {
        this.goodfly = goodfly;
    }
    public BadFly getBadfly() {
        return badfly;
    }
    public void setBadfly(BadFly badfly) {
        this.badfly = badfly;
    }
    public NotFly getNotfly() {
        return notfly;
    }
    public void setNotfly(NotFly notfly) {
        this.notfly = notfly;
    }
    public Bird(String name, int age) {
        this.name = name;
        this.age = age;
        goodfly=new GoodFly();
        badfly=new BadFly();
        notfly=new NotFly();
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    
}

測試：

package top.littlepage.designPattern.Strategy;

public class Test {
    public static void main(String[] args) {
        Bird b=new Bird("小鳥",2);
        System.out.print(b.getName());
        b.getGoodfly().fly();
        
        System.out.print(b.getName());
        b.getBadfly().fly();
        
        System.out.print(b.getName());
        b.getNotfly().fly();
    }
}

控制檯截圖

策略模式(strategy)利用介面進行抽象，利用實體進行實現抽象，再做出環境進行實現具體的實體

在我們面向物件後，經常利用這種設計模式進行程式設計，應該是比較簡單的一種模式