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:
- 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);
}
- 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 !");
}
}
}
- 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;
}
}
- 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....
