Java OOPs 面试题与答案

问题 11. What is the purpose of the 'static' keyword in Java?

The 'static' keyword is used to create class-level variables and methods. These belong to the class rather than instances of the class.

Example:

static int count = 0;
static void increment() { count++; }

问题 12. Explain the concept of composition in Java.

Composition involves creating complex objects by combining simpler objects. It allows for better code organization and reusability.

Example:

class Car {
  Engine engine;
  // other properties and methods
}

问题 13. What is the purpose of the 'interface' in Java?

An interface in Java is a collection of abstract methods that defines a contract for classes to implement. It supports multiple inheritances and is often used for achieving abstraction.

Example:

interface Printable { void print(); }

问题 14. Explain the 'diamond problem' and how Java solves it.

The 'diamond problem' occurs in multiple inheritance when a class inherits from two classes that have a common ancestor. In Java, this is avoided by allowing a class to implement multiple interfaces.

问题 15. What is the purpose of the 'final' method in Java?

A 'final' method in Java cannot be overridden by subclasses. It is used to prevent modification of a method in a subclass.

Example:

class Parent {
  final void display() { /* method implementation */ }
}