狀態模式：允許對象在內部狀態改變時改變它的行為，對象看起來好像修改了它的類。將每種狀態封裝成獨立的類，并將動作委托給代表當前狀態的對象，當糖果機處于不同的狀態時，你投入25￥會得到不同的行為。
策略模式是除了繼承之外一種彈性替代方案，通過組合不同的對象來改變行為。
狀態模式是不用在context中放置許多條件判斷的替代方案，通常將行為包裝進狀態中，通過在context中簡單的改變狀態對象來改變context的行為。
狀態的改變可以放在context中也可以放在狀態類中控制，而且狀態類可以被多個Context實例共享,前提是狀態對象不能持有他們自己的內部狀態，否則不能共享。想要共享狀態，需要把每個狀態都指定到靜態的實例變量中。狀態模式會導致類的數目大增。

public class GumballMachine {
//all the states of a machine
State soldOutState;
State noQuarterState;
State hasQuarterState;
State soldState;
State winnerState;

//there is no candy in the machine at the beginning
State state = soldOutState;

int count = 0; // count for the number of candy

public GumballMachine(int numberGumballs) {
soldOutState = new SoldOutState(this);
noQuarterState = new NoQuarterState(this);
hasQuarterState = new HasQuarterState(this);
soldState = new SoldState(this);
winnerState = new WinnerState(this);
this.count = numberGumballs;
if(numberGumballs > 0){//如果有糖果
state = noQuarterState;
}
}

public void insertQuarter(){
state.insertQuarter(); //委托給具體的狀態實例來執行
}
public void ejectQuarter(){
state.ejectQuarter();
}
public void turnCrank(){
state.turnCrank();
state.dispense();???
}
public State getHasQuarterState() {
// TODO Auto-generated method stub
return hasQuarterState;
}

public void setState(State state) {
// TODO Auto-generated method stub
this.state = state;
}

void releaseBall(){
System.out.println("A gumball comes rolling out of slot...");
if (count != 0) {
count = count-1;
}
}

public State getNoQuarterState() {
// TODO Auto-generated method stub
return noQuarterState;
}

public State getSoldOutState() {
return soldOutState;
}

public State getSoldState() {
return soldState;
}

public int getCount() {
return count;
}

public void setCount(int count) {
this.count = count;
}

public State getWinnerState() {
// TODO Auto-generated method stub
return winnerState;
}

}
//所有狀態的接口，里面包括狀態轉移的方法
public interface State {
public void insertQuarter();
public void ejectQuarter();
public void turnCrank();
public void dispense();???
}

public class SoldState implements State {
GumballMachine gumballMachine;
public SoldState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}

@Override
public void dispense() {
// TODO Auto-generated method stub
gumballMachine.releaseBall();
if (gumballMachine.getCount()>0) {
gumballMachine.setState(gumballMachine.getNoQuarterState());
} else {
System.out.println("Oops, out of gumballs!");
gumballMachine.setState(gumballMachine.getSoldOutState());
}
}

@Override
public void ejectQuarter() {
// TODO Auto-generated method stub
System.out.println("sorry, you already turned the crank");
}

@Override
public void insertQuarter() {
// TODO Auto-generated method stub
System.out.println("Please wait, we're already giving you a gumball");
}

@Override
public void turnCrank() {
// TODO Auto-generated method stub
System.out.println("Turning the crank twice doesn't get you another gumball!");
}

}
//implement the state which there is no 25$ in the machine
public class NoQuarterState implements State{
GumballMachine gumballMachine;

public NoQuarterState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}

@Override
public void dispense() {
// if there is no money
System.out.println("You need to pay first!");
}

@Override
public void ejectQuarter() {
// 沒有給錢就不能退錢
System.out.println("You haven't insert a quarter");
}

@Override
public void insertQuarter() {
// 接收25$然后改變狀態為HasQuarterState
System.out.println("You insert a quarter");
gumballMachine.setState(gumballMachine.getHasQuarterState());
}

@Override
public void turnCrank() {
// 沒給錢就沒有糖果
System.out.println("You turned, but there's no quarter");
}

}

轉載于:https://www.cnblogs.com/aquar/archive/2010/05/27/3451450.html

總結

以上是生活随笔為你收集整理的head first Design Pattern State的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。