帶有靜態初始值設定項的Java嵌套類

Question

正在閱讀名為Emergent Design的書以及關於單例的主題...

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

然后日食不斷抱怨靜態{}

正在閱讀Java，這些類應該具有多個靜態初始化程序。 那么如何使以上工作呢？

---

/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

為了在靜態上下文中合法引用字段，該字段必須在上下文本地，或者在類中聲明為靜態。 如果要引用singleton ，則需要將其聲明為static 。

Answer 2

您需要將private static Object singleton;放置private static Object singleton; 靜態塊不能修改非靜態變量。