定義

當一個對象的內(nèi)在狀態(tài)改變時允許改變其行為，這個對象看起來像是改變了其類

public interface TvState {
    public void next();
    public void pre();
    public void up();
    public void down();
}

package com.qc.state;

public class PowerOffState implements TvState {

    @Override
    public void next() {
        // TODO Auto-generated method stub

    }

    @Override
    public void pre() {
        // TODO Auto-generated method stub

    }

    @Override
    public void up() {
        // TODO Auto-generated method stub

    }

    @Override
    public void down() {
        // TODO Auto-generated method stub

    }

}

package com.qc.state;

public class PowerOnState implements TvState {

    @Override
    public void next() {
        // TODO Auto-generated method stub
        System.out.println("下一首");
    }

    @Override
    public void pre() {
        // TODO Auto-generated method stub
        System.out.println("上一首");
    }

    @Override
    public void up() {
        // TODO Auto-generated method stub
        System.out.println("上");
    }

    @Override
    public void down() {
        // TODO Auto-generated method stub
        System.out.println("下");
    }

}

package com.qc.state;

public interface PowerController {
    public void powerOn();
    public void powerOff();
}

package com.qc.state;

public class Tv implements PowerController {
    TvState mTvState;

    @Override
    public void powerOn() {
        // TODO Auto-generated method stub
        setTvState(new PowerOnState());
    }

    @Override
    public void powerOff() {
        // TODO Auto-generated method stub
        setTvState(new PowerOffState());
    }

    public void setTvState(TvState mTvState) {
        this.mTvState = mTvState;
    }

    public void next() {
        mTvState.next();
    }

    public void pre() {
        mTvState.pre();
    }

    public void up() {
        mTvState.up();
    }

    public void down() {
        mTvState.down();
    }

}

package com.qc.state;

public class Client {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Tv mTv = new Tv();
        mTv.powerOn();
        mTv.next();
        mTv.pre();
        mTv.up();
        mTv.down();
    }

}

使用

1、一個對象的行為取決于它的狀態(tài)。并且它必須在運行時根據(jù)狀態(tài)改變它的行為。
2、代碼中包含大量與對象狀態(tài)有關(guān)的條件語句，例如，一個操作中含有龐大的多分支語句（if-else或switch-case），且這些分支依賴于該對象的狀態(tài)。