java compiled classes contain dollar signs
JavaClassCompilationJava Problem Overview
I've been using Eclipse as my IDE. I also use it to export my application into a JAR file. When I look at my classes in the JAR file, a few of my classes contain the name of that class, a dollar sign, then a number. For example:
Find$1.class
Find$2.class
Find$3.class
Find.class
I've noticed it does this on bigger classes. Is this because the classes get so big, it compiles it into multiple classes? I've googled and looked on multiple forums, and search the Java documentation but have not found anything even related to it. Could someone explain?
Java Solutions
Solution 1 - Java
Inner classes, if any present in your class, will be compiled and the class file will be ClassName$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:
TestInnerOuterClass.class
TestInnerOuterClass$TestInnerChild.class
TestInnerOuterCasss$1.class
Update:
Using anonymous class is not considered a bad practice ,it just depends on the usage.
Check this discussion on SO
Solution 2 - Java
This is because you have anonymous classes within this larger class. They get compiled using this naming convention.
See https://stackoverflow.com/questions/7778556/the-anonymous-class-conundrum
Solution 3 - Java
In addition to the above cases presented by @mprabhat, the other cases could be:
- if you class contain a enum variable a separate class would be generated for that too. The name of the .class generated would be ClassName$Name_of_enum.
- 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
- 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.
Solution 4 - Java
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.