What can you throw in Java?

Question

Conventional wisdom says you can only throw objects that extend Throwable in Java, but is it possible to disable the bytecode verifier and get Java to compile a

Answer 1

As mentioned in John's answer, you can disable verification (placing the class on the bootclasspath should also work ), load and execute a class throwing a non-Throwable class successfully.

Surprisingly, it doesn't necessarily lead to a crash!

As long as you don't call Throwable methods implicitly or explicitly, everything will work perfectly fine:

.source ThrowObject.j
.class public ThrowObject
.super java/lang/Object

.method public ()V
    aload_0
    invokenonvirtual java/lang/Object/()V
    return
.end method

.method public static main([Ljava/lang/String;)V

    new java/lang/Object
    dup
    invokenonvirtual java/lang/Object/()V

  BeforeThrow:
    athrow

  AfterThrow:

    return

  CatchThrow:

    getstatic java/lang/System/out Ljava/io/PrintStream;
    ldc "Thrown and catched Object successfully!"
    invokevirtual java/io/PrintStream.println(Ljava/lang/String;)V
    return

  .catch all from BeforeThrow to AfterThrow using CatchThrow
.end method

Result:

% java -Xverify:none ThrowObject
Thrown and catched Object successfully!