设计模式-策略模式(十二)

策略模式,又叫政策模式

• 用意: 针对一组算法,抽象出一个接口,每个算法实现这个接口,使得客户端可以相互替换,关键点是算法替换

动态的让一个对象从许多的行为中选择一种实现.

使用的太频繁了.
类图:

策略模式.png

示例代码:

1. 先创建一个接口,需要实现的算法

package com.byedbl.strategy;

/**
 *  The public interface to support varies arithmetic
 */
public interface Strategy {
    public void drawText(String s, int lineWidth, int lineCount);
}

2. 再分别对这个算法搞两种不同的实现

package com.byedbl.strategy; /**
 *  A concrete strategy to draw a text by the width of line
 */
public class StrategyA implements Strategy {
    public StrategyA() {
    }
    public void drawText(String text, int lineWidth, int lineCount) {
        if(lineWidth > 0) {
            int len = text.length();
            int start = 0;
            System.out.println("----- String length is :" + len + ", line width is :" + lineWidth);
            while(len > 0) {
                if(len <= lineWidth) {
                    System.out.println(text.substring(start));
                } else {
                    System.out.println(text.substring(start, start+lineWidth));
                }
                len = len - lineWidth;
                start += lineWidth;
            }
        } else {
            System.out.println("line width can not < 1 !");
        }
    }
}

另一种实现

package com.byedbl.strategy;

public class StrategyB implements Strategy {
    public StrategyB() {
    }
    public void drawText(String text, int lineWidth, int lineCount) {
        if(lineCount > 0) {
            int len = text.length();
            //System.out.println(Math.ceil(len/lineCount));
            lineWidth = (int)Math.ceil(len/lineCount) + 1;
            int start = 0;
            System.out.println("-----  There are " + lineCount + " Line, " + lineWidth + "char per line -----");
            while(len > 0) {
                if(len <= lineWidth) {
                    System.out.println(text.substring(start));
                } else {
                    System.out.println(text.substring(start, start+lineWidth));
                }
                len = len - lineWidth;
                start += lineWidth;
            }
        } else {
            System.out.println("line count can not < 1 !");
        }
    }
}

3. 有个Context类对引用.其实没有的话就客户端直接调也可以

package com.byedbl.strategy; /**
 *  The context user used
 */
public class Context  {
    private Strategy strategy = null;
    private int lineWidth;
    private int lineCount;
    private String text;
    
    public Context() {
        lineWidth = 10;
        lineCount = 0;
    }
    public void setStrategy(Strategy s) {
        if(s != null) {
            strategy = s;
        }
    }
    public void drawText() {
        strategy.drawText(text, lineWidth, lineCount);
    }
    public void setText(String str) {
        text = str;
    }
    public void setLineWidth(int width) {
        lineWidth = width;
    }
    public void setLineCount(int count) {
        lineCount = count;
    }
    public String getText() {
        return text;
    }
}

4. 客户端用法

package com.byedbl.strategy;

/**
 *  A test client
 */
public class Test  {
    public static void main(String[] args) {
        int lineCount = 4;
        int lineWidth = 12;
        
        Context myContext = new Context();
        StrategyA strategyA = new StrategyA();
        StrategyB strategyB = new StrategyB();
        String s = "This is a test string ! This is a test string ! This is a test string ! This is a test string ! This is a test string ! This is a test string !";
        myContext.setText(s);
        myContext.setLineWidth(lineWidth);
        myContext.setStrategy(strategyA);
        myContext.drawText();

        myContext.setLineCount(lineCount);
        myContext.setStrategy(strategyB);
        myContext.drawText();
    }
}

换一种策略就一种实现了...很实用,,,很经典,,,很牛逼....