Shell script that unpacks and runs a Java bug. Verification does not ensure static correctness of interface types.

javabugdemo.bash

echo "interface I1 { }" > I1.java
echo "interface I2 { }" > I2.java
echo "interface I3 { }" > I3.java
echo "class I1I2 implements I1, I2 { }" > I1I2.java_good
echo "class I1I2 implements I1     { }" > I1I2.java_bad
echo "class I1I3I2 implements I1, I3, I2 { }" > I1I3I2.java

cat > tricky.java <<'//EOF'
class tricky {
 I2 i2;
 static I2 si2;

 boolean isI2(Object x) {
    return (x == null) || (x instanceof I2);
  }
  
  void expectsI2(I2 x) {
    String result = isI2(x) ? "pass" : "fail";
    System.err.println(result);
  }

  I2 cloaksI2(boolean b, I1I2 x, I1I3I2 y) {
    I2 i2 = b ? (I2) x : (I2) y;
    this.i2 = i2;
    si2 = i2;
    expectsI2(i2);
    return i2;
  }

  public static void main(String args[]) {
    tricky t = new tricky();
    t.expectsI2(t.cloaksI2(true, new I1I2(), new I1I3I2())); 
    t.expectsI2(t.i2);
    t.expectsI2(si2);
  }
}
//EOF

cp I1I2.java_good I1I2.java
javac tricky.java

# You might expect this here would cause verification problems in the future.
cp I1I2.java_bad I1I2.java  
javac I1I2.java

# But no...
java -verify -Xfuture -cp . tricky