- 定義：
當(dāng)一個(gè)對(duì)象的內(nèi)在狀態(tài)改變時(shí)允許改變其行為，這個(gè)對(duì)象看起來(lái)像是改變了其類。
狀態(tài)模式主要解決的是當(dāng)控制一個(gè)對(duì)象狀態(tài)的條件表達(dá)式過(guò)于復(fù)雜時(shí)的情況。把狀態(tài)的判斷邏輯轉(zhuǎn)移到表示不同狀態(tài)的一系列類中，可以把復(fù)雜的判斷邏輯簡(jiǎn)化口四。 -
UML:
image.png - 模型：
投幣的糖果機(jī)，糖果機(jī)根據(jù)內(nèi)部的狀態(tài)秦陋，表現(xiàn)出是否可以投幣蔓彩，是否可以退幣，是否要掉落糖果等驳概，例如赤嚼，在未投幣的狀態(tài)下是不能退幣的，在已投幣未掉落糖果的情況下也不能再次投幣的顺又。而狀態(tài)模式就能很好的解決這樣復(fù)雜的邏輯判斷更卒，解決的方式是將這些邏輯轉(zhuǎn)移到多個(gè)類中。
//首先我們抽象出所有的狀態(tài)下都應(yīng)該有的行為稚照。
public interface State {
//投硬幣
public void insertCoin();
//返回硬幣
public void returnCoin();
//轉(zhuǎn)動(dòng)把手 出糖果
public void turnCrank();
//掉落糖果
public void dispense();
//輸出狀態(tài)
public void printstate();
}
//構(gòu)建一個(gè)糖果機(jī)
public class CandyMachine {
State mSoldOutState;
State mOnReadyState;
State mHasCoin;
State mSoldState;
State mWinnerState;
private State state;
private int count = 0;
//組合多種狀態(tài)
public CandyMachine(int count) {
this.count = count;
mSoldOutState = new SoldOutState(this);
mOnReadyState = new OnReadyState(this);
mHasCoin = new HasCoin(this);
mSoldState = new SoldState(this);
mWinnerState = new WinnerState(this);
if (count > 0) {
state = mOnReadyState;
} else {
state = mSoldOutState;
}
}
//糖果機(jī)的行為完全受當(dāng)前的狀態(tài)決定
public void setState(State state) {
this.state = state;
}
public void insertCoin() {
state.insertCoin();
}
public void returnCoin() {
state.returnCoin();
}
public void turnCrank() {
state.turnCrank();
state.dispense();
}
void releaseCandy() {
if (count > 0) {
count = count - 1;
System.out.println("a candy rolling out!");
}
}
public int getCount() {
return count;
}
public void printstate() {
state.printstate();
}
}
//糖果機(jī)可用狀態(tài)
public class OnReadyState implements State {
private CandyMachine mCandyMachine;
public OnReadyState(CandyMachine mCandyMachine){
this.mCandyMachine=mCandyMachine;
}
//當(dāng)前狀態(tài)只能投入硬幣蹂空，不提供其他行為
@Override
public void insertCoin() {
System.out
.println("you have inserted a coin,next,please turn crank!");
//當(dāng)投入硬幣后，更改糖果機(jī)的狀態(tài)
mCandyMachine.setState(mCandyMachine.mHasCoin);
}
@Override
public void returnCoin() {
System.out.println("you haven't inserted a coin yet!");
}
@Override
public void turnCrank() {
System.out.println("you turned,but you haven't inserted a coin!");
}
@Override
public void dispense() {}
@Override
public void printstate() {
System.out.println("***OnReadyState***");
}
}
//有硬幣的狀態(tài)
public class HasCoin implements State {
private CandyMachine mCandyMachine;
public HasCoin(CandyMachine mCandyMachine) {
this.mCandyMachine = mCandyMachine;
}
@Override
public void insertCoin() {
System.out.println("you can't insert another coin!");
}
//當(dāng)前狀態(tài)可用回退硬幣
@Override
public void returnCoin() {
System.out.println("coin return!");
mCandyMachine.setState(mCandyMachine.mOnReadyState);
}
//當(dāng)前狀態(tài)可用轉(zhuǎn)動(dòng)把手掉落糖果
@Override
public void turnCrank() {
System.out.println("crank turn...!");
Random ranwinner=new Random();
int winner=ranwinner.nextInt(10);
//設(shè)置一個(gè)幸運(yùn)糖果果录，還有一次獲取糖果的機(jī)會(huì)
if(winner==0){
mCandyMachine.setState(mCandyMachine.mWinnerState);
}else{
mCandyMachine.setState(mCandyMachine.mSoldState);
}
}
@Override
public void dispense() {}
@Override
public void printstate() {
System.out.println("***HasCoin***");
}
}
//銷售狀態(tài)
public class SoldState implements State {
private CandyMachine mCandyMachine;
public SoldState(CandyMachine mCandyMachine){
this.mCandyMachine=mCandyMachine;
}
@Override
public void insertCoin() {
System.out.println("please wait!we are giving you a candy!");
}
@Override
public void returnCoin() {
System.out.println("you haven't inserted a coin yet!");
}
@Override
public void turnCrank() {
System.out
.println("we are giving you a candy,turning another get nothing,!");
}
@Override
public void dispense() {
//掉落糖果
mCandyMachine.releaseCandy();
//根據(jù)當(dāng)前糖果的數(shù)量設(shè)置下一個(gè)狀態(tài)
if (mCandyMachine.getCount() > 0) {
mCandyMachine.setState(mCandyMachine.mOnReadyState);
} else {
System.out.println("Oo,out of candies");
mCandyMachine.setState(mCandyMachine.mSoldOutState);
}
}
@Override
public void printstate() {
System.out.println("***SoldState***");
}
}
//得到幸運(yùn)糖果的狀態(tài)上枕，可以再次獲得一次糖果
public class WinnerState implements State {
private CandyMachine mCandyMachine;
public WinnerState(CandyMachine mCandyMachine) {
this.mCandyMachine = mCandyMachine;
}
@Override
public void insertCoin() {
System.out.println("please wait!we are giving you a candy!");
}
@Override
public void returnCoin() {
System.out.println("you haven't inserted a coin yet!");
}
@Override
public void turnCrank() {
System.out
.println("we are giving you a candy,turning another get nothing,!");
}
@Override
public void dispense() {
mCandyMachine.releaseCandy();
if (mCandyMachine.getCount() == 0) {
mCandyMachine.setState(mCandyMachine.mSoldOutState);
} else {
System.out.println("you are a winner!you get another candy!");
//再次獲得糖果。但是不能再是幸運(yùn)糖果了
mCandyMachine.releaseCandy();
if (mCandyMachine.getCount() > 0) {
mCandyMachine.setState(mCandyMachine.mOnReadyState);
} else {
System.out.println("Oo,out of candies");
mCandyMachine.setState(mCandyMachine.mSoldOutState);
}
}
}
@Override
public void printstate() {
System.out.println("***WinnerState***");
}
}
//賣光了狀態(tài)
public class SoldOutState implements State {
private CandyMachine mCandyMachine;
public SoldOutState(CandyMachine mCandyMachine){
this.mCandyMachine=mCandyMachine;
}
@Override
public void insertCoin() {
System.out.println("you can't insert coin,the machine sold out!");
}
@Override
public void returnCoin() {
System.out
.println("you can't return,you haven't inserted a coin yet!");
}
@Override
public void turnCrank() {
System.out.println("you turned,but there are no candies!");
}
@Override
public void dispense() {}
@Override
public void printstate() {
System.out.println("***SoldOutState***");
}
}
測(cè)試
public class MainTest {
public static void main(String[] args) {
CandyMachine mCandyMachine = new CandyMachine(6);
mCandyMachine.printstate();
mCandyMachine.insertCoin();
mCandyMachine.printstate();
mCandyMachine.turnCrank();
mCandyMachine.printstate();
mCandyMachine.insertCoin();
mCandyMachine.printstate();
mCandyMachine.turnCrank();
mCandyMachine.printstate();
}
}
- 總結(jié)：
如果是按照傳統(tǒng)的面向?qū)ο蟮姆绞饺鹾悖枪麢C(jī)自己維護(hù)當(dāng)前的狀態(tài)辨萍，那么糖果機(jī)對(duì)外提供的每個(gè)方法都會(huì)去switch每一個(gè)狀態(tài)，做不同的判斷處理返弹，還要考慮當(dāng)前的糖果個(gè)數(shù)锈玉，想想邏輯就很復(fù)雜，很容易出錯(cuò)义起。而狀態(tài)模式拉背，將這些復(fù)雜的判斷都轉(zhuǎn)移到每個(gè)狀態(tài)類中，狀態(tài)類最清楚那些方法該怎么處理默终。糖果機(jī)只需要關(guān)心自己有幾種狀態(tài)椅棺，提供那些方法使用抡诞。除此之外，狀態(tài)模式很像策略模式土陪，其實(shí)他們的UML是一樣的，但意圖卻完全不一樣肴熏，策略模式是讓用戶指定更換的策略算法鬼雀，而狀態(tài)模式是狀態(tài)在滿足一定條件下的自動(dòng)更換，用戶無(wú)法指定狀態(tài)蛙吏，最多只能設(shè)置初始狀態(tài)源哩。
總的來(lái)說(shuō)：態(tài)模式關(guān)鍵是各個(gè)狀態(tài)子類必須知道下一個(gè)狀態(tài)是啥，且要把邏輯判斷轉(zhuǎn)移到各個(gè)狀態(tài)子類中鸦做，客戶端不需要了解狀態(tài)遷移的順序励烦，但是策略目的是針對(duì)單一算法的運(yùn)行時(shí)替換，客戶端需要事先了解策略泼诱，主動(dòng)去選擇合適的策略坛掠，不存在狀態(tài)的自動(dòng)遷移！
