JAVA设计模式之状态模式

状态模式：允许对象在内部状态改变时改变它的行为，对象看起来好像修改了它的类。

例子：实现一个machine，有红绿蓝三种状态，有last和next两个按钮，按下按钮时会切换状态。

public interface State
{    
    public void last();
    public void next();
    public String getState();
}

public class RedState implements State
{
    Machine machine;
    
    public RedState(Machine machine)
    {
        this.machine = machine;
    }

    public void last() 
    {
        machine.setState(new BlueState(machine));
    }

    public void next() 
    {
        machine.setState(new GreenState(machine));
    }

    public String getState() 
    {
        return "Red";
    }
}

public class GreenState implements State
{
    Machine machine;
    
    public GreenState(Machine machine)
    {
        this.machine = machine;
    }

    public void last() 
    {
        machine.setState(new RedState(machine));
    }

    public void next() 
    {
        machine.setState(new BlueState(machine));
    }

    public String getState() 
    {
        return "Green";
    }
}

public class BlueState implements State
{
    Machine machine;
    
    public BlueState(Machine machine)
    {
        this.machine = machine;
    }

    public void last() 
    {
        machine.setState(new GreenState(machine));
    }

    public void next() 
    {
        machine.setState(new RedState(machine));
    }

    public String getState() 
    {
        return "Blue";
    }
}

public class Machine 
{
    private State state;

    public String getState()
    {
        return state.getState();
    }

    public void setState(State state) 
    {
        this.state = state;
    }
    
    public void last()
    {
        state.last();
    }
    
    public void next()
    {
        state.next();
    }
}

public class Test 
{
    private static final int interval = 500; 
    
    public static void main(String[] args) throws InterruptedException  
    {
        Machine machine = new Machine();
        machine.setState(new RedState(machine));
        System.out.println("last: ");
        for(int i = 0; i < 3; i++)
        {
            System.out.println("state："+machine.getState());
            machine.last();
            Thread.sleep(interval);
        }      
        machine.setState(new RedState(machine));
        System.out.println("
next: ");
        for(int i = 0; i < 3; i++)
        {
            System.out.println("state："+machine.getState());
            machine.next();
            Thread.sleep(interval);
        }         
    }
}