解決的問題

開發(fā)一個保存圖片的功能，保存圖片前，需要先對圖片進行壓縮、添加濾鏡等處理。

代碼

Compressor:

package com.cong.designpattern.strategy;

public interface Compressor {
    public void compress(String fileName);
}

JpegCompressor:

package com.cong.designpattern.strategy;

public class JpegCompressor implements Compressor{
    @Override
    public void compress(String fileName) {
        System.out.println("Compress to Jpeg");
    }
}

PngCompressor:

package com.cong.designpattern.strategy;

public class PngCompressor implements Compressor{
    @Override
    public void compress(String fileName) {
        System.out.println("Compress to PNG");
    }
}

Filter:

package com.cong.designpattern.strategy;

public interface Filter {
    public void filter(String fileName);
}

BlackAndWhiteFilter:

package com.cong.designpattern.strategy;

public class BlackAndWhiteFilter implements Filter{
    @Override
    public void filter(String fileName) {
        System.out.println("Filter with black and white");
    }
}

ImageStore:

package com.cong.designpattern.strategy;

public class ImageStore {
    public ImageStore(Compressor compressor, Filter filter) {
        this.compressor = compressor;
        this.filter = filter;
    }

    private Compressor compressor;
    private Filter filter;

    public void store(String fileName) {
        compressor.compress(fileName);
        filter.filter(fileName);
    }
}

Test code:

ImageStore imageStore = new ImageStore(new PngCompressor(), new BlackAndWhiteFilter());
imageStore.store("a");

UML

Strategy Pattern UML

好處

滿足單一職責原則。ImageStore應該只有保存圖片的職責，通過組合的方式把壓縮圖片、添加濾鏡等操作封裝到其他相應的類。
Strategy Pattern和State Pattern非常像，原理是一樣的?？梢岳斫鉃镾tate Pattern是只有一種Strategy的Strategy Pattern。