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享元模式

實現

ShapeFactory有一個CircleHashMap，其中鍵名為Circle對象的顏色。 無論何時接收到請求，都會創建一個特定顏色的圓。ShapeFactory檢查它的HashMap中的circle對象，如果找到Circle對象，則返回該對象，否則將創建一個存儲在hashmap中以備後續使用的新對象，並把該對象返回到客戶端。

FlyWeightPatternDemo，我們的演示類使用ShapeFactory來獲取Shape對象。 它將向ShapeFactory傳遞信息（red / green / blue/ black / white），以便獲取它所需對象的顏色。

步驟1

Shape.java

```public interface Shape {
void draw();
}
```

步驟2

Circle.java

```public class Circle implements Shape {
private String color;
private int x;
private int y;

public Circle(String color){
this.color = color;
}

public void setX(int x) {
this.x = x;
}

public void setY(int y) {
this.y = y;
}

}

@Override
public void draw() {
System.out.println("Circle: Draw() [Color : " + color
+", x : " + x +", y :" + y +", radius :" + radius);
}
}
```

步驟3

ShapeFactory.java

```import java.util.HashMap;

public class ShapeFactory {
private static final HashMap<String, Shape> circleMap = new HashMap();

public static Shape getCircle(String color) {
Circle circle = (Circle)circleMap.get(color);

if(circle == null) {
circle = new Circle(color);
circleMap.put(color, circle);
System.out.println("Creating circle of color : " + color);
}
return circle;
}
}
```

步驟4

FlyweightPatternDemo.java

```public class FlyweightPatternDemo {
private static final String colors[] =
{ "Red", "Green", "Blue", "White", "Black" };
public static void main(String[] args) {

for(int i=0; i < 20; ++i) {
Circle circle =
(Circle)ShapeFactory.getCircle(getRandomColor());
circle.setX(getRandomX());
circle.setY(getRandomY());
circle.draw();
}
}
private static String getRandomColor() {
return colors[(int)(Math.random()*colors.length)];
}
private static int getRandomX() {
return (int)(Math.random()*100 );
}
private static int getRandomY() {
return (int)(Math.random()*100);
}
}
```

步驟5

```Creating circle of color : Black
Circle: Draw() [Color : Black, x : 36, y :71, radius :100
Creating circle of color : Green
Circle: Draw() [Color : Green, x : 27, y :27, radius :100
Creating circle of color : White
Circle: Draw() [Color : White, x : 64, y :10, radius :100
Creating circle of color : Red
Circle: Draw() [Color : Red, x : 15, y :44, radius :100
Circle: Draw() [Color : Green, x : 19, y :10, radius :100
Circle: Draw() [Color : Green, x : 94, y :32, radius :100
Circle: Draw() [Color : White, x : 69, y :98, radius :100
Creating circle of color : Blue
Circle: Draw() [Color : Blue, x : 13, y :4, radius :100
Circle: Draw() [Color : Green, x : 21, y :21, radius :100
Circle: Draw() [Color : Blue, x : 55, y :86, radius :100
Circle: Draw() [Color : White, x : 90, y :70, radius :100
Circle: Draw() [Color : Green, x : 78, y :3, radius :100
Circle: Draw() [Color : Green, x : 64, y :89, radius :100
Circle: Draw() [Color : Blue, x : 3, y :91, radius :100
Circle: Draw() [Color : Blue, x : 62, y :82, radius :100
Circle: Draw() [Color : Green, x : 97, y :61, radius :100
Circle: Draw() [Color : Green, x : 86, y :12, radius :100
Circle: Draw() [Color : Green, x : 38, y :93, radius :100
Circle: Draw() [Color : Red, x : 76, y :82, radius :100
Circle: Draw() [Color : Blue, x : 95, y :82, radius :100
```