Java, A Beginner's Guide, 5th Edition, 5th Edition

Reference Variables and Assignment

In an assignment operation, object reference variables act differently than do variables of a primitive type, such as int. When you assign one primitive-type variable to another, the situation is straightforward. The variable on the left receives a copy of the value of the variable on the right. When you assign one object reference variable to another, the situation is a bit more complicated because you are changing the object that the reference variable refers to. The effect of this difference can cause some counterintuitive results. For example, consider the following fragment:

At first glance, it is easy to ...