Java中抽象类用法与注意点实例详解

abstract class Person    //定义一抽象类Person
{
  String name;
  int age;
  String occupation;
  public abstract String talk(); // 声明一抽象方法talk()
}
class Student extends Person  // Student类继承自Person类
{
  public Student( String name, int age, String occupation ) {
    this.name = name;
    this.age = age;
    this.occupation = occupation;
  }
  @Override
  public String talk()  // 实现talk()方法
  {
    return "学生——>姓名：" + name + "，年龄：" + age + "，职业：" + occupation;
  }
}
class Worker extends Person  // Worker类继承自Person类
{
  public Worker( String name, int age, String occupation ) {
    this.name = name;
    this.age = age;
    this.occupation = occupation;
  }
  public String talk()   // 覆写talk()方法
  {
    return "工人——>姓名：" + name + ",年龄：" + age + ",职业:" + occupation;
  }
}
public class AbstractClassDemo {
  public static void main( String[] args ) {
    Student s = new Student("张三", 20, "学生"); //创建Student类对象s
    Worker w = new Worker("李四", 30, "工人");  //创建Worker类对象w
    Person s1 = new Student("王五", 20, "学生"); //通过向上转换的方法创建Student类对象s
    Person w1 = new Worker("马六", 30, "工人");  //通过向上转换的方法创建Worker类对象w
    System.out.println(s.talk());     //调用被实现的方法
    System.out.println(w.talk());
    System.out.println(s1.talk());
    System.out.println(w1.talk());
  }
}

abstract class Person {
  String name;
  int age;
  String occupation;
  public Person( String name, int age, String occupation ) {
    this.name = name;
    this.age = age;
    this.occupation = occupation;
  }
  public abstract String talk();
}
class Student extends Person {
  public Student( String name, int age, String occupation ) {  // 在这里必须明确调用抽象类中的构造方法
    super(name, age, occupation);
  }
  public String talk() {
    return "学生——>姓名：" + name + "，年龄：" + age + "，职业：" + occupation;
  }
}
public class AbstractConstructor {
  public static void main( String[] args ) {
    Student s = new Student("张三", 18, "学生");//第1种方式创建对象s
    Person s1 = new Student("李四", 18, "学生");//第2种方式创建对象s1
    System.out.println(s.talk());
    System.out.println(s1.talk());
  }
}