Java Trivia point 2

Encapsulation refers to data hiding, the key is that the method in the class must not be allowed to access other classes of the instance domain, the program only through the object's methods and object data to interact.

Among the classes, the most common relationships are:

• Dependency: A method of one class manipulates another class object
• Aggregation: An object that contains objects of some other class
• Inheritance: Subclasses and Parent classes

Local variables cannot be initialized to NULL, you need to set new or null manually, and class variables are automatically initialized (0,false,null).

Do not write accessor methods that return references to mutable objects, which allows an external program to modify the instance domain. The correct approach is to return the clone of the instance variable.

A method can access private data for all objects of the owning class

The final modifier is most often applied to a field of a primitive type or an immutable class. For a mutable class, final can only indicate that the reference cannot point to another object.

Java parameter passing is always a value pass, including an object reference.

Java Trivia point 2