Constructor must call super() or this() before return in method

Question

I am getting this error:

Exception in thread "Thread-0" java.lang.VerifyError: Constructor must call super() or this() before return in method JGame.Util.KeyboardMap.<init>()V at offset 0
        at JGame.Room.Room.keyboardEventTests(Room.java:81)
        at JGame.Room.Room.run(Room.java:54)
        at java.lang.Thread.run(Thread.java:722)

When my application loads, it calls this method right away (KeyboardMap.map is an empty HashMap).

Here is the Method (Line 54 calls this method this.keyboardEventTests(); ):

protected void keyboardEventTests(){
    for(Map.Entry ap : KeyboardMap.map.entrySet()){ // Line 81
        Mapping mp = (Mapping)ap.getValue();
        if(mp.doing){
            mp.run();
        }
    }
}

And here is the KeyboardMap class.

package JGame.Util;

import java.util.HashMap;
import java.util.Map;

public class KeyboardMap{

    public static Map<String, Mapping> map = new HashMap<>();

    public static void set(String key, Boolean value, Runnable run){
        Mapping mp = new Mapping();
        mp.doing = value;
        mp.run = run;
        KeyboardMap.map.put(key, mp);
    }

    public static Mapping get(String key){
        return KeyboardMap.map.get(key);
    }
}

Why am I getting that error, and how can I get rid of it?

Answer 1

Why am I getting that error, and how can I get rid of it?

The big clue is that this is a VerifyError , not a compilation error. What this means is that the JVM has found a bytecode file in which one of the constructors is not chaining properly. These are (in effect) a malformed bytecodes.

How can that happen?

• Well it CAN'T happen in a Java class that is (just) compiled in the normal way. The compiler will automatically insert an implicit super() call into any constructor that doesn't explicitly chain.

• If this is Java code, then either:

  • the class was compiled using broken compiler (unlikely!), or

  • something has tweaked the bytecodes after compilation.

• If it was some other language, then the first suspect would be the "other language to bytecode" compilation process.

I think you are getting this problem because your unit tests is using a mocking framework, and the mocking framework is using "byte code engineering" to inject something into the classes under test. The code that is doing this has "made a mistake" and the result is bytecodes that won't compile.

---

This was apparently fixed by a rebuild, but that doesn't contradict this explanation. A rebuild could clear out broken instrumentation code injected by the mocking framework. And next time around, the framework could "get it right".

Answer 2

Just override the default contructor by adding

public KeyboardMap() {
}

to the KeyboardMap class. It will work.

Answer 3

I had the same problem, and it was caused by a very strange thing: In NetBeans, i use editor fold to fold long codes:

// <editor-fold desc="SOME DESCRIPTION">
  ...
  ...
// </editor-fold>

And it appeared that in one of such my folds i had forgotten to write the beginning of fold, like this:

  ...
  ...
// </editor-fold>

Correcting this solved my problem . Strange, because this is just a comment and it's for NetBeans

Answer 4

在我的例子中，在buildTypes下关闭build.gradle中的minify有帮助。

minifyEnabled false