更改main方法后，将TreeMap实例传递给构造函数的行为是什么

Question

Suppose I have the setup:

TreeMap<Long,ClassA> derkMap = new TreeMap<Long,ClassA>();
derkMap.put(1L,new ClassA());

Note that ClassA has public void doSomething() , which when called will change the instance's state permanently (in what precise way is irrelevant to this question). Note that once doSomething() is called, ClassA has a public boolean hasItBeenCalled() which will return true ; else it'll return false if doSomething() has not been called.

If I run the following sequence in my main method:

• (1) Pass derkMap instance to constructor of some ClassB (ie instantiate in my main method ClassB objectB = new ClassB(derkMap); ).
• (2) Call derkMap.get(1L).doSomething(); from main method.
• (3) Within the instance of ClassB (ie, objectB ), try derkMap.get(1L).hasItBeenCalled() .

Will (3) return true or false ?

Answer 1

Everything in Java is pass by value. Recommended reading: this and its follow up .

Edit: even more recommended reading: Is Java "pass-by-reference" or "pass-by-value"?

Another edit: This answer no longer makes sense as the question was edited, but I'm leaving it because I think it's what the OP is actually confused about.

Answer 2

It should return true. That's because when you pass map as a parameter of classB its reference is copied by value and it still points to the original map. If you call methods of the element inside map it still executes those methods on the orginal map.

EDIT

By the way, after I answered this question it took me 3 minutes to verify it by writing sample code. I'm just wondering why you haven't tried it yourself.