1. 策略设计模式初衷
减少代码冗余，降低代码之间的耦合度。同时保证代码的可维护性。 Positive: - Often reduces long lists of conditions - Avoid duplicate code - Keep class changes from other class changes - Can hide complicated/ secret code from the user Negative: Increased number of Objects/Classes
2. 策略实际模式应用场景
当我们想要定义一组算法，而且这些算法所要表现的的内容很相似时。如果在每个父类定义该算法的普适版本，然后在子类中覆盖override该方法这样一方面增加了代码的冗余度，另一方面违背了子类方法应该相互之间不同这一设计原则。但我们想要动态改变对象的某种行为，且该行为有几种可供选择项时。
3. 具体UML图及解释
这里的Animal作为一个base class, derived class–包括Dog和Bird可以直接继承该父类，完成相应的功能，但这不是好的设计准则。因为这样引入了大量冗余代码，且违背了OOD的封装特性。
4. 一个具体的demo
package com.fqyuan.strategy;
public interface Flys {
public String
fly();
}
class FlyFast implements Flys {
@Override
public String
fly() {
return "Flying fast!";
}
}
class FlySlow implements Flys {
@Override
public String
fly() {
return "Flying slowly!";
}
}
class NotFly implements Flys {
@Override
public String
fly() {
return "Unable to fly!";
}
}
package com.fqyuan.strategy;
public class Animal {
private String name;
public Flys flyType;
public void setName(String name) {
this.name = name;
}
public String
getName() {
return name;
}
public String
tryToFly() {
return flyType.fly();
}
public void setFlyType(Flys newFlyType) {
flyType = newFlyType;
}
@Override
public String
toString() {
return name;
}
}
package com.fqyuan.strategy;
public class Dog extends Animal {
public Dog(String name) {
this.setName(name);
flyType =
new NotFly();
}
}
package com.fqyuan.strategy;
public class Cat extends Animal {
public Cat(String name) {
setName(name);
this.flyType =
new FlyFast();
}
}
package com.fqyuan.strategy;
public class StrategyDemo {
public static void main(String[] args) {
Animal dog =
new Dog(
"Rick");
Cat cat =
new Cat(
"Kitty");
System.out.println(dog +
" " + dog.tryToFly());
System.out.println(cat +
" " + cat.tryToFly());
dog.setFlyType(
new FlySlow());
System.out.println(dog +
" " + dog.tryToFly());
}
}
Rick Unable to fly!
Kitty Flying fast!
Rick Flying slowly!
