我原本以爲在對鄉村的一切事物都很容易，但是每次我一回頭就有更多變更的請求紛至沓來。我快崩潰了！----當小編讀到這段話的時候，甚是感慨，設計模式的世界真的不是那麼容易弄懂的，好在我還在學習。
基本常識：策略模式和狀態模式是雙胞胎，在出生時才分開。策略模式是圍繞可以互換的算法來創建成功業務的。然而，狀態走的是更崇高的路，它通過改變對象內部的狀態來幫助對象控制自己的行爲。
我們先來看下對象村的大家，這次又想出了什麼。他們發現只要在糖果機裏裝上CPU，就可以增加銷量、通過網絡監測庫存，並且能準確地得知客戶的滿意度。所有，就有了下面的這個設想：
狀態機101
我們如何從狀態圖得到真正的代碼呢？下面是一個實現狀態機的簡單介紹
首先，找出所有的狀態：
我們有：沒有25分錢、有25分錢、糖果售罄、售出糖果四個狀態
接下來，創建一個實例變量來持有目前的狀態，然後定義每個狀態的值:
final static int SOLD_OUT = 0; final static int NO_QUARTER = 1; final static int HAS_QUARTER = 2; final static int SOLD = 3; int state = SOLD_OUT;static int SOLD_OUT = 0;
final static int NO_QUARTER = 1;
final static int HAS_QUARTER = 2;
final static int SOLD = 3;
int state = SOLD_OUT;
現在，我們將所有系統中可以發生的動作整合起來：
投入25分錢、退回25分錢、轉動曲柄、發放糖果
現在，我們創建一個類，它的作用就像是一個狀態機。對每一個動作，我們都創建了一個對應的方法，這些方法利用條件語句來決定在每個狀態內什麼行爲是恰當的。比如對“投入25分錢”這個動作來說，我們可以把對應方法寫成下面的樣子:
public void insertQuarter() { if (state == HAS_QUARTER) { System.out.println("You can't insert another quarter"); } else if (state == NO_QUARTER) { state = HAS_QUARTER; System.out.println("You inserted a quarter"); } else if (state == SOLD_OUT) { System.out.println("You can't insert a quarter, the machine is old out"); } else if (state == SOLD) { System.out.println("Please wait, we're already giving you a gumball"); }}
if (state == HAS_QUARTER) {
System.out.println("You can't insert another quarter");
} else if (state == NO_QUARTER) {
state = HAS_QUARTER;
System.out.println("You inserted a quarter");
} else if (state == SOLD_OUT) {
System.out.println("You can't insert a quarter, the machine is old out");
} else if (state == SOLD) {
System.out.println("Please wait, we're already giving you a gumball");
}
}
寫下代碼
現在我們來實現糖果機。我們知道要利用實例變量持有當前的狀態，然後需要處理所有可能發生的動作、行爲和狀態的轉換。我們需要實現的動過包括：投入25分錢、退回25分錢、轉動曲柄和發放糖果；也要檢查糖果是否售罄。
public class GumballMachine { final static int SOLD_OUT = 0; final static int NO_QUARTER = 1; final static int HAS_QUARTER = 2; final static int SOLD = 3; int state = SOLD_OUT; int count = 0; public GumballMachine(int count) { this.count = count; if (count > 0) { state = NO_QUARTER; } } // 當有25分錢投進來，就會執行這裏 public void insertQuarter() { if (state == HAS_QUARTER) { System.out.println("You can't insert another quarter"); } else if (state == NO_QUARTER) { state = HAS_QUARTER; System.out.println("You inserted a quarter"); } else if (state == SOLD_OUT) { System.out.println("You can't insert a quarter, the machine is sold out"); } else if (state == SOLD) { System.out.println("Please wait, we're already giving you a gumball"); } } // 現在，如果顧客試着退回25分錢 public void ejectQuarter() { if (state == HAS_QUARTER) { System.out.println("Quarter returned"); state = NO_QUARTER; } else if (state == NO_QUARTER) { System.out.println("You haven't inserted a quarter"); } else if (state == SOLD) { System.out.println("Sorry, you already turned the crank"); } else if (state == SOLD_OUT) { System.out.println("You can't eject, you haven't inserted a quarter yet"); } } // 顧客試着轉動曲柄 public void turnCrank() { if (state == SOLD) { System.out.println("Turning twice doesn't get you another gumball!"); } else if (state == NO_QUARTER) { System.out.println("You turned but there's no quarter"); } else if (state == SOLD_OUT) { System.out.println("You turned, but there are no gumballs"); } else if (state == HAS_QUARTER) { System.out.println("You turned..."); state = SOLD; dispense(); } } // 調用此方法，發放糖果 private void dispense() { if (state == SOLD) { System.out.println("A gumball comes rolling out the slot"); count = count - 1; if (count == 0) { System.out.println("Oops, out of gumballs!"); state = SOLD_OUT; } else { state = NO_QUARTER; } } else if (state == NO_QUARTER) { System.out.println("You need to pay first"); } else if (state == SOLD_OUT) { System.out.println("No gumball dispensed"); } else if (state == HAS_QUARTER) { System.out.println("No gumball dispensed"); } } public void refill(int numGumBalls) { this.count = numGumBalls; state = NO_QUARTER; } public String toString() { StringBuffer result = new StringBuffer(); result.append("\nMighty Gumball, Inc."); result.append("\nJava-enabled Standing Gumball Model #2004\n"); result.append("Inventory: " + count + " gumball"); if (count != 1) { result.append("s"); } result.append("\nMachine is "); if (state == SOLD_OUT) { result.append("sold out"); } else if (state == NO_QUARTER) { result.append("waiting for quarter"); } else if (state == HAS_QUARTER) { result.append("waiting for turn of crank"); } else if (state == SOLD) { result.append("delivering a gumball"); } result.append("\n"); return result.toString(); }}class GumballMachine {
final static int SOLD_OUT = 0;
final static int NO_QUARTER = 1;
final static int HAS_QUARTER = 2;
final static int SOLD = 3;
int state = SOLD_OUT;
int count = 0;
public GumballMachine(int count) {
this.count = count;
if (count > 0) {
state = NO_QUARTER;
}
}
// 當有25分錢投進來，就會執行這裏
public void insertQuarter() {
if (state == HAS_QUARTER) {
System.out.println("You can't insert another quarter");
} else if (state == NO_QUARTER) {
state = HAS_QUARTER;
System.out.println("You inserted a quarter");
} else if (state == SOLD_OUT) {
System.out.println("You can't insert a quarter, the machine is sold out");
} else if (state == SOLD) {
System.out.println("Please wait, we're already giving you a gumball");
}
}
// 現在，如果顧客試着退回25分錢
public void ejectQuarter() {
if (state == HAS_QUARTER) {
System.out.println("Quarter returned");
state = NO_QUARTER;
} else if (state == NO_QUARTER) {
System.out.println("You haven't inserted a quarter");
} else if (state == SOLD) {
System.out.println("Sorry, you already turned the crank");
} else if (state == SOLD_OUT) {
System.out.println("You can't eject, you haven't inserted a quarter yet");
}
}
// 顧客試着轉動曲柄
public void turnCrank() {
if (state == SOLD) {
System.out.println("Turning twice doesn't get you another gumball!");
} else if (state == NO_QUARTER) {
System.out.println("You turned but there's no quarter");
} else if (state == SOLD_OUT) {
System.out.println("You turned, but there are no gumballs");
} else if (state == HAS_QUARTER) {
System.out.println("You turned...");
state = SOLD;
dispense();
}
}
// 調用此方法，發放糖果
private void dispense() {
if (state == SOLD) {
System.out.println("A gumball comes rolling out the slot");
count = count - 1;
if (count == 0) {
System.out.println("Oops, out of gumballs!");
state = SOLD_OUT;
} else {
state = NO_QUARTER;
}
} else if (state == NO_QUARTER) {
System.out.println("You need to pay first");
} else if (state == SOLD_OUT) {
System.out.println("No gumball dispensed");
} else if (state == HAS_QUARTER) {
System.out.println("No gumball dispensed");
}
}
public void refill(int numGumBalls) {
this.count = numGumBalls;
state = NO_QUARTER;
}
public String toString() {
StringBuffer result = new StringBuffer();
result.append("\nMighty Gumball, Inc.");
result.append("\nJava-enabled Standing Gumball Model #2004\n");
result.append("Inventory: " + count + " gumball");
if (count != 1) {
result.append("s");
}
result.append("\nMachine is ");
if (state == SOLD_OUT) {
result.append("sold out");
} else if (state == NO_QUARTER) {
result.append("waiting for quarter");
} else if (state == HAS_QUARTER) {
result.append("waiting for turn of crank");
} else if (state == SOLD) {
result.append("delivering a gumball");
}
result.append("\n");
return result.toString();
}
}
現在，讓我們進入一個小小的內部測試，看下是否符合了要求。
public class WinnerState implements State { GumballMachine gumballMachine; public WinnerState(GumballMachine gumballMachine) { this.gumballMachine = gumballMachine; } public void insertQuarter() { System.out.println("Please wait, we're already giving you a Gumball"); } public void ejectQuarter() { System.out.println("Please wait, we're already giving you a Gumball"); } public void turnCrank() { System.out.println("Turning again doesn't get you another gumball!"); } public void dispense() { gumballMachine.releaseBall(); if (gumballMachine.getCount() == 0) { gumballMachine.setState(gumballMachine.getSoldOutState()); } else { gumballMachine.releaseBall(); System.out.println("YOU'RE A WINNER! You got two gumballs for your quarter"); if (gumballMachine.getCount() > 0) { gumballMachine.setState(gumballMachine.getNoQuarterState()); } else { System.out.println("Oops, out of gumballs!"); gumballMachine.setState(gumballMachine.getSoldOutState()); } } } public void refill() { } public String toString() { return "despensing two gumballs for your quarter, because YOU'RE A WINNER!"; }}class WinnerState implements State {
GumballMachine gumballMachine;
public WinnerState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
public void insertQuarter() {
System.out.println("Please wait, we're already giving you a Gumball");
}
public void ejectQuarter() {
System.out.println("Please wait, we're already giving you a Gumball");
}
public void turnCrank() {
System.out.println("Turning again doesn't get you another gumball!");
}
public void dispense() {
gumballMachine.releaseBall();
if (gumballMachine.getCount() == 0) {
gumballMachine.setState(gumballMachine.getSoldOutState());
} else {
gumballMachine.releaseBall();
System.out.println("YOU'RE A WINNER! You got two gumballs for your quarter");
if (gumballMachine.getCount() > 0) {
gumballMachine.setState(gumballMachine.getNoQuarterState());
} else {
System.out.println("Oops, out of gumballs!");
gumballMachine.setState(gumballMachine.getSoldOutState());
}
}
}
public void refill() { }
public String toString() {
return "despensing two gumballs for your quarter, because YOU'RE A WINNER!";
}
}
運行結果比較長，在這裏就不進行打印啦，需要的朋友請自行根據代碼進行執行。
變更需求來了，需要新設計
現在，客戶要求當曲柄轉動時，有10%的機率掉下來的是兩顆糖果（多送你一顆），那你應該怎麼做呢？
我們的計劃是這樣的：不要維護我們現有的代碼，我們重寫它以便於將狀態對象封裝在各自的類中，然後在動作發生時委託給當前狀態。所以，我們要做的事情就是：
首先，我們定義一個State接口。在這個接口中，糖果機的每個動作都有一個對應的方法
然後爲機器中的每個狀態實現狀態類。這些將負責在對應的狀態下進行機器的行爲
最後，我們要擺脫舊的條件代碼，取而代之的方式是，將動作委託到狀態類
你將會看到，我們不僅遵守了設計原則，實際上我們還實現了狀態模式。接下來，我們定義狀態接口和類，如下：
好了，到現在爲止，我們下一步肯定是要去實現怎麼改造了，對吧。在這裏呢，給大家先留着，先去思考思考，如何進行改造。思路有了，類圖有了，就看你怎麼想啦。我們下一次揭曉。
