What's the difference between Name and CanonicalName? [duplicate]

Question

What is the difference between Java's Class.getName() and Class.getCanonicalName()?

Reptant

Also See #15203497 – Strigose

@Anush funny, I didn't see that one when looking it up, which is only a month older than mine. Thanks – Reptant

Answer 1

Consider the following program:

package org.test.stackoverflow;

public class CanonicalName {

  public static void main(String[] args) {
    CanonicalName cn = new CanonicalName();
    cn.printClassNames();
  }

  private Anonymous anony;
  private MyAnony myAnony;

  public CanonicalName() {
    anony = new Anonymous() {
      public void printInterface() {
        System.out.println("Anony Name: " + getClass().getName());
        System.out.println("Anony CanonicalName: " + getClass().getCanonicalName());
      }
    };
    myAnony = new MyAnony();
  }

  public void printClassNames() {
    System.out.println("CanonicalName, Name: " + getClass().getName());
    System.out.println("CanonicalName, CanonicalName: " + getClass().getCanonicalName());
    anony.printInterface();
    myAnony.printInterface();
  }

  private static interface Anonymous {
    public void printInterface();
  }

  private static class MyAnony implements Anonymous {
    public void printInterface() {
      System.out.println("MyAnony Name: " + getClass().getName());
      System.out.println("MyAnony CanonicalName: " + getClass().getCanonicalName());
    }
  }
}

Output:

CanonicalName, Name: org.test.stackoverflow.CanonicalName
CanonicalName, CanonicalName: org.test.stackoverflow.CanonicalName
Anony Name: org.test.stackoverflow.CanonicalName$1
Anony CanonicalName: null
MyAnony Name: org.test.stackoverflow.CanonicalName$MyAnony
MyAnony CanonicalName: org.test.stackoverflow.CanonicalName.MyAnony

So it seems that for base classes, they return the same thing. For inner classes, getName() uses the $ naming convention (i.e. what is used for .class files), and getCanonicalName() returns what you would use if you were trying to instantiate the class. You couldn't do that with a (little-a) anonymous class, so that's why getCanonicalName() returns null.

Reptant

It's impossible to find answer to your own question in just seconds. Looks like deception. Times of the question and the answer are exactly the same. – Ranket

@MaciejZiarko There's a checkbox at the bottom "answer your own question, Q&A style. I wanted to add my recent discovery to the knowledge base in SO, because I couldn't find it anywhere. – Reptant

For future reference, don't name the class after the very concept you're trying to explore/portray... – Effluvium