Why does DJ v3.7.7.81 generate weird-looking static fields like class$exercise$MyClass and static me

[Bruce .J Sam]

I have use DJ v3.7.7.81 to decompile MyClass.class and
MyClass$1.class. The result is so werid-looking. How can I do if I want
to recompile the decomplied class?

//MyClass.class decompile result.
//Decompiler options: packimports(3) noinners
package exercise;

public interface MyClass
{

public abstract void perform();

public static final String CONTROL_TYPE =
(MyClass$1.class$exercise$MyClass != null ?
MyClass$1.class$exercise$MyClass : (MyClass$1.class$exercise$MyClass =
MyClass$1._mthclass$("exercise.MyClass"))).getName();

}

//MyClass$1.class decompile result.
//Decompiler options: packimports(3) noinners

package exercise;

class MyClass$1
{

static Class _mthclass$(String s)
{
try
{
return Class.forName(s);
}
catch(ClassNotFoundException classnotfoundexception)
{
throw new
NoClassDefFoundError(classnotfoundexception.getMessage());
}
}

static Class class$exercise$MyClass; /* synthetic field */
}