Question

public class Strange1 {
  public static void main(String[] args) {
    try {
      Missing m = new Missing();
    } catch (java.lang.NoClassDefFoundError ex) {
      System.out.println("Got it!");
    }
  }
}

public class Strange2 {
  public static void main(String[] args) {
    Missing m;
    try {
      m = new Missing();
    } catch (java.lang.NoClassDefFoundError ex) {
      System.out.println("Got it!");
    }
  }
}

class Missing {
  Missing() { }
}

If you run Strange1 and Strange2 after deleting Missing.class, Strange1 will throw NoClassDefFoundError; but Strange2 will print Got it！

Can anyone explain that? Thanks.

updated:

java bytecode for Strange1 :

     0  new info.liuxuan.test.Missing [16]
     3  dup
     4  invokespecial info.liuxuan.test.Missing() [18]
     7  astore_1 [m]
     8  goto 20
    11  astore_1 [ex]
    12  getstatic java.lang.System.out : java.io.PrintStream [19]
    15  ldc <String "Got it!"> [25]
    17  invokevirtual java.io.PrintStream.println(java.lang.String) : void [27]
    20  return
      Exception Table:
        [pc: 0, pc: 8] -> 11 when : java.lang.NoClassDefFoundError
      Line numbers:
        [pc: 0, line: 14]
        [pc: 11, line: 15]
        [pc: 12, line: 16]
        [pc: 20, line: 18]
      Local variable table:
        [pc: 0, pc: 21] local: args index: 0 type: java.lang.String[]
        [pc: 8, pc: 11] local: m index: 1 type: info.liuxuan.test.Missing
        [pc: 12, pc: 20] local: ex index: 1 type: java.lang.NoClassDefFoundError

java bytecode for Strange2 :

     0  new info.liuxuan.test.Missing [16]
     3  dup
     4  invokespecial info.liuxuan.test.Missing() [18]
     7  astore_1 [m]
     8  goto 20
    11  astore_2 [ex]
    12  getstatic java.lang.System.out : java.io.PrintStream [19]
    15  ldc <String "Got it!"> [25]
    17  invokevirtual java.io.PrintStream.println(java.lang.String) : void [27]
    20  return
      Exception Table:
        [pc: 0, pc: 8] -> 11 when : java.lang.NoClassDefFoundError
      Line numbers:
        [pc: 0, line: 15]
        [pc: 11, line: 16]
        [pc: 12, line: 17]
        [pc: 20, line: 19]
      Local variable table:
        [pc: 0, pc: 21] local: args index: 0 type: java.lang.String[]
        [pc: 8, pc: 11] local: m index: 1 type: info.liuxuan.test.Missing
        [pc: 12, pc: 20] local: ex index: 2 type: java.lang.NoClassDefFoundError

There is only one place is different:

11  astore_1 [ex]

and

11  astore_2 [ex]

updated again:

Everyone can try it in eclipse.

Answer 1

Prior to saying anything, i doub’t this code won’t even compile. because when compiler cannot find a class (Since its deleted). may be you are getting an error when trying to compile it using javac command. if thats the case its pretty normal and in no way its weird.

and let me add an another point.. check your imports, to contain Missing class. if it is there then remove it. and tell us whats happening.