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public enum FontEffect {
    BOLD, ITALIC, SUPERSCRIPT, SUBSCRIPT, STRIKETHROUGH
}

public final class FontData {
    /**
     * A weak hash map will drop unused references to FontData.
     * Values have to be wrapped in WeakReferences,
     * because value objects in weak hash map are held by strong references.
     */
    private static final WeakHashMap<FontData, WeakReference<FontData>> FLY_WEIGHT_DATA =
        new WeakHashMap<FontData, WeakReference<FontData>>();
    private final int pointSize;
    private final String fontFace;
    private final Color color;
    private final Set<FontEffect> effects;

    private FontData(int pointSize, String fontFace, Color color, EnumSet<FontEffect> effects) {
        this.pointSize = pointSize;
        this.fontFace = fontFace;
        this.color = color;
        this.effects = Collections.unmodifiableSet(effects);
    }

    public static FontData create(int pointSize, String fontFace, Color color,
        FontEffect... effects) {
        EnumSet<FontEffect> effectsSet = EnumSet.noneOf(FontEffect.class);
        for (FontEffect fontEffect : effects) {
            effectsSet.add(fontEffect);
        }
        // We are unconcerned with object creation cost, we are reducing overall memory consumption
        FontData data = new FontData(pointSize, fontFace, color, effectsSet);

        // Retrieve previously created instance with the given values if it (still) exists
        WeakReference<FontData> ref = FLY_WEIGHT_DATA.get(data);
        FontData result = (ref != null) ? ref.get() : null;

        // Store new font data instance if no matching instance exists
        if (result == null) {
            FLY_WEIGHT_DATA.put(data, new WeakReference<FontData> (data));
            result = data;
        }
        // return the single immutable copy with the given values
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof FontData) {
            if (obj == this) {
                return true;
            }
            FontData other = (FontData) obj;
            return other.pointSize == pointSize && other.fontFace.equals(fontFace)
                && other.color.equals(color) && other.effects.equals(effects);
        }
        return false;
    }

    @Override
    public int hashCode() {
        return (pointSize * 37 + effects.hashCode() * 13) * fontFace.hashCode();
    }

    // Getters for the font data, but no setters. FontData is immutable.
}

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public interface Flyweight {
    void action(int arg);
}

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public class FlyweightImpl implements Flyweight {
    @Override
    public void action(int arg) {
        System.out.println("参数值："+arg);
    }
}

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import java.util.HashMap;
import java.util.Map;

public class FlyweightFactory {
    private static Map flyweights = new HashMap();

    public FlyweightFactory(String arg){
        flyweights.put(arg,new FlyweightImpl());
    }

    public static Flyweight getFlyweight(String key){
        if(flyweights.get(key)==null){
            flyweights.put(key,new FlyweightImpl());
        }
        return (Flyweight) flyweights.get(key);
    }

    public static int getSize(){
        return flyweights.size();
    }
}

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public class Test {
    public static void main(String[] args) {
        Flyweight fly1 = FlyweightFactory.getFlyweight("a");
        fly1.action(1);

        Flyweight fly2 = FlyweightFactory.getFlyweight("a");
        System.out.println(fly1==fly2);

        Flyweight fly3 = FlyweightFactory.getFlyweight("b");
        fly3.action(2);

        Flyweight fly4 = FlyweightFactory.getFlyweight("c");
        fly4.action(3);

        Flyweight fly5 = FlyweightFactory.getFlyweight("d");
        fly5.action(4);

        System.out.println(FlyweightFactory.getSize());
    }
}

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参数值：1
true
参数值：2
参数值：3
参数值：4
4