Broken bytecode when using generic type in if-statement condition

Issue #270 resolved
Jesper Öqvist created an issue

ExtendJ 8.1.0-21-g42ca049 Java SE 7

ExtendJ generates unexecutable bytecode for the following program:

// Test if-statement with generic condition.
// .result: EXEC_PASS
public class Test {
  public static void main(String[] args) {
    run(204 + 1);

  static void run(int value) {
    Container<Boolean> con = new Container<Boolean>(value % 100 == 4);
    if (con.get()) {
      System.out.println("should be false");
    if (!con.get()) {
    System.out.println("should be false");


class Container<T> {
  private final T value;

  public Container(T value) {
    this.value = value;

  T get() {
    return value;

Expected result: should be executable.

Actual result: fails to run:

    [junit] [FAIL] runTest[run/generics/container_01](tests.extendj.TestJava7)
    [junit] Error output files differ expected:<[]> but was:<[Exception in thread "main" java.lang.VerifyError: Bad type on operand stack
    [junit] Exception Details:
    [junit]   Location:
    [junit] @28: invokevirtual
    [junit]   Reason:
    [junit]     Type 'java/lang/Object' (current frame, stack[0]) is not assignable to 'java/lang/Boolean'
    [junit]   Current Frame:
    [junit]     bci: @28
    [junit]     flags: { }
    [junit]     locals: { integer, 'Container' }
    [junit]     stack: { 'java/lang/Object' }

Comments (1)

  1. Jesper Öqvist reporter

    Fix error in conditional branch unboxing

    If the expression in a conditional branch had a generic type, that does not have java.lang.Boolean as its erasure, then the expression has to be cast to java.lang.Boolean before unboxing to boolean.

    fixes #270 (bitbucket) fixes #271 (bitbucket) fixes #272 (bitbucket)

    → <<cset 329e3d61a7ef>>

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