Java的嵌套類

Question

正在讀的書叫緊急設計和單身的話題......

public class MyApp { 
private class SingletonHolder { 
    public Object singleton; 
    static { 
    singleton = new Object(); 
    } 
} 
} 

然後蝕不斷抱怨靜態{}

在讀的Java，類應該可以有多個靜態初始值設定項。那麼我怎樣才能做出上述工作呢？

---

/tmp/jc_4873/MyApp.java:5: non-static variable singleton cannot be referenced from a static context 
    singleton = new Object(); 
^
/tmp/jc_4873/MyApp.java:4: inner classes cannot have static declarations 
    static { 
^
2 errors 

---

public class MyApp { 
private class SingletonHolder { 
    public static Object singleton; 
    static { 
    singleton = new Object(); 
    } 
} 
} 

/tmp/jc_8488/MyApp.java:3: inner classes cannot have static declarations 
    public static Object singleton; 
        ^
/tmp/jc_8488/MyApp.java:4: inner classes cannot have static declarations 
    static { 
^
2 errors 

---

public class MyApp { 
private static class SingletonHolder { 
    public static Object singleton; 
    static { 
    singleton = new Object(); 
    } 
} 
} 

Answer 1

對於要在靜態上下文中合法引用的字段，該字段必須是上下文本地的或者在類中聲明爲靜態的。如果你想參考singleton，你需要聲明它static。

Answer 2

你需要把private static Object singleton;靜態塊不能修改非靜態變量。