explain pass by value and reference

JLS When the method ... is invoked ..., the values of the actual argument expressions initialize newly created parameter variables Means: always by value. It may be confusing, but if you try to pass a reference, then this is just a regular variable and a copy is passed. You can try this, If you pass a reference to a method and inside the method you assign a new object to your reference var (change the reference itself, not the object behind it). You'll see that nothing will change in main. It still references the same old object it referenced before invoking the method.

public static void main(String[] args) {
    String reference = "abc";
    testReference(reference);
    // but the reference didn't change in main, still pointing to abc
    System.out.println("reference in main: " + reference);
}

private static void testReference(String reference) {
    // reference is now pointing to a new object "def"
    reference = "def";
    System.out.println("reference in test: " + reference);
}