Java 编译的类包含美元符号

我一直在使用 Eclipse 作为我的 IDE。我还使用它将应用程序导出到一个 JAR 文件中。当我查看 JAR 文件中的类时，我的一些类包含该类的名称、一个美元符号和一个数字。例如:

Find$1.class
Find$2.class
Find$3.class
Find.class

我注意到在更大的课堂上会这样。这是因为类变得太大了，它会将其编译成多个类吗？我已经在多个论坛上谷歌和搜索了 Java 文档，但是没有找到任何与之相关的东西。有人能解释一下吗？

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最佳答案

Inner classes, if any present in your class, will be compiled and the class file will be ClassName$InnerClassName. In case of Anonymous inner classes, it will appear as numbers. Size of the Class (Java Code) doesn't lead to generation of multiple classes.

E.g. given this piece of code:

public class TestInnerOuterClass {
class TestInnerChild{


}


Serializable annoymousTest = new Serializable() {
};
}

Classes which will be generated will be:

  1. TestInnerOuterClass.class
  2. TestInnerOuterClass$TestInnerChild.class
  3. TestInnerOuterCasss$1.class

Update:

Using anonymous class is not considered a bad practice ,it just depends on the usage.

Check this discussion on SO

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This is because you have anonymous classes within this larger class. They get compiled using this naming convention.

See The Anonymous Class Conundrum

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To answer your comment about are anonymous classes bad. They are most definately not. Consider this to assign an action listener to a JButton:

JButton button = new JButton(...);
button.addActionListener(new ActionListener() { ... });

or this to do a case insensitive sort by the "name" property

Collections.sort( array, new Comparator<Foo>() {
public int compare(Foo f1, Foo f2) {
return f1.getName().toLowerCase().compareTo(f2.getName().toLowerCase());
}
});

You'll also see a lot of Runnable and Callable done as anonymous classes.

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In addition to the above cases presented by @mprabhat, the other cases could be:

  1. if you class contain a enum variable a separate class would be generated for that too. The name of the .class generated would be ClassName$Name_of_enum.
  2. If your class X is inheriting i.e. extending another class Y, then there would be a .class generated with the name ClassName$1.class or ClassName$1$1.class
  3. If your class X is implementing an interface Y, then there would be a .class generated with the name ClassName$1.class or ClassName$1$1.class.

These cases are derivations of my inspection on .class files in jar.


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