匿名内部类：返回一个匿名内部类的实例

Question

我正在通过《Thinking in java 4th Edition》这本书自学Java。

当我开始尝试书中的一个示例时，它给出了编译器错误。

https://github.com/BruceEckel/TIJ4-code/blob/master/examples/innerclasses/Parcel7.java

//: innerclasses/Parcel7.java
// Returning an instance of an anonymous inner class.

public class Parcel7 {
  public Contents contents() {
    return new Contents() { // Insert a class definition
      private int i = 11;
      public int value() { return i; }
    }; // Semicolon required in this case
  }
  public static void main(String[] args) {
    Parcel7 p = new Parcel7();
    Contents c = p.contents();
  }
} ///:~

.\Parcel7.java:4: error: cannot find symbol
    public Contents contents() {
           ^
  location: class Parcel7
.\Parcel7.java:5: error: cannot find symbol
        return new Contents() {
                   ^
  symbol:   class Contents
  location: class Parcel7
.\Parcel7.java:13: error: cannot find symbol
        Contents c = p.contents();
        ^
  symbol:   class Contents
  location: class Parcel7
3 errors
PS S:\Java Learning\001. Hello> javac .\Parcel7.java
.\Parcel7.java:2: error: cannot find symbol
    public Contents contents() {
           ^
  symbol:   class Contents
  location: class Parcel7
.\Parcel7.java:3: error: cannot find symbol
      return new Contents() { // Insert a class definition
                 ^
  symbol:   class Contents
  location: class Parcel7
.\Parcel7.java:10: error: cannot find symbol
      Contents c = p.contents();
      ^
  symbol:   class Contents
  location: class Parcel7
3 errors

我有什么想念的吗？

Answer 1

此匿名类声明创建一个匿名类，它是类Contents 的子类型。

查看错误，我假设您没有在任何地方定义名为Contents 的命名类。如果您已经拥有该类，则它可能没有正确导入。