设计模式12:状态模式
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状态模式解决的是控制一个对象状态转移的表达式过于复杂的情况,把状态的判断逻辑转移表示到不同状态的一系列类中,可以把复杂的逻辑简化。
状态模式的好处是将特定状态的行为局部化,从而将不同状态的行为分割开来。
将特定状态的行为都放入一个对象中,由于与状态有关的代码都存在在具体的对象类中,因此定义新的子类可以很容易的实现增加新的状态和转换。
uml图:
State及其子类
public abstract class State { public abstract void writeProgram(Work work); } public class BeforeNoon extends State { @Override public void writeProgram(Work work) { if(work.getHour() < 12){ System.out.println("现在是" + Integer.toString(work.getHour())+ "点,工作!"); } else{ work.setState(new Noon()); work.writeProgram(); } } } public class Noon extends State { @Override public void writeProgram(Work work) { if(work.getHour() < 14){ System.out.println("现在是" + Integer.toString(work.getHour())+ "点,午休!"); } else{ work.setState(new AfterNoon()); work.writeProgram(); } } } public class AfterNoon extends State { @Override public void writeProgram(Work work) { if(work.getHour() < 17){ System.out.println("现在是" + Integer.toString(work.getHour())+ "点,工作!"); } else{ work.setState(new Night()); work.writeProgram(); } } } public class Night extends State { @Override public void writeProgram(Work work) { if(work.isFinished()){ System.out.println("现在是" + Integer.toString(work.getHour())+ "点,下班!"); } else{ System.out.println("现在是" + Integer.toString(work.getHour())+ "点,加班!"); } } }
Work
public class Work { private int hour = 0; private boolean isFinished = false; private State state = new BeforeNoon(); public int getHour() { return hour; } public void setHour(int hour) { this.hour = hour; } public boolean isFinished() { return isFinished; } public void setFinished(boolean isFinished) { this.isFinished = isFinished; } public State getState() { return state; } public void setState(State state) { this.state = state; } public void writeProgram() { state.writeProgram(this); } }
Demo
public class StateDemo { public static void main(String[] args) { Work work = new Work(); for(int hour = 8; hour < 22; hour++){ work.setHour(hour); if(hour == 19){ work.setFinished(true); } work.writeProgram(); } } }
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