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状态模式

状态（State）模式：对有状态的对象，把复杂的“判断逻辑”提取到不同的状态对象中，允许状态对象在其内部状态发生改变时改变其行为。

案例

模拟不同的上课状态转换：

public interface ClassState {void study();ClassState next();
}

public class MathClassState implements ClassState{@Overridepublic void study() {System.out.println("数学课想睡觉");}@Overridepublic ClassState next() {return new PEClassState();}
}

public class PEClassState implements ClassState{@Overridepublic void study() {System.out.println("体育课打起精神");}@Overridepublic ClassState next() {return new AfterClassState();}
}

public class AfterClassState implements ClassState{@Overridepublic void study() {System.out.println("放学了很开心");}@Overridepublic ClassState next() {return new MathClassState();}
}

public class Student {private ClassState state;public Student(ClassState state){this.state = state;}public void study(){state.study();}public void nextState(){this.state = state.next();}
}

测试：

public class Main {public static void main(String[] args) {Student student = new Student(new MathClassState());student.study();student.nextState();student.study();student.nextState();student.study();}
}