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System.out.println("name:" + ps.getName() + ";" + "grade:"+ ((PrimaryStudent) ps).getGrade());请问你这句代码的((PrimaryStudent) ps).getGrade()为什么(PrimaryStudent) ps.getGrade()不行，一定是要将ps也用括号包起来才可以打印。
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System.out.println("name:" + ps.getName() + ";" + "grade:"+ ((PrimaryStudent) ps).getGrade());请问你这句代码的((PrimaryStudent) ps).getGrade()为什么(PrimaryStudent) ps.getGrade()不行，一定是要将ps也用括号包起来才可以打印。
狠美味2013
/**
* 定义PrimaryStudent，从Student继承，新增grade字段:
*
* @author yuanxiaowen
*
*/
public class ExtendsExample {
public static void main(String[] args) {
Person p = new Person("小明", 12);
Student s = new Student("小红", 20, 99);
// TODO: 定义PrimaryStudent，从Student继承，新增grade字段:
Student ps = new PrimaryStudent("小军", 9, 100, 5);
System.out.println(p.getName());
System.out.println(s.getName());
System.out.println("name:" + ps.getName() + ";" + "score:"
+ ps.getScore());
System.out.println("name:" + ps.getName() + ";" + "grade:"
+ ((PrimaryStudent) ps).getGrade());
}
}
/**
* 给Person增加构造方法; 给Person增加重载方法setName(String, String)
*
* @author yuanxiaowen
*/
public class Person {
private String name;
private int age;
public Person() {
}
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return this.age;
}
public void setAge(int age) {
this.age = age;
}
public void setName(String prename, String lastname) {
this.name = prename + " " + lastname;
}
}
/**
* Student
*
* @author yuanxiaowen
*
*/
public class Student extends Person {
protected int score;
public Student(String name, int age, int score) {
super(name, age);
this.score = score;
}
public int getScore() {
return score;
}
}
/**
* 定义PrimaryStudent，从Student继承，新增grade字段:
*
* @author yuanxiaowen
*
*/
public class PrimaryStudent extends Student {
// TODO: 定义PrimaryStudent，从Student继承，新增grade字段:
protected int grade;
public PrimaryStudent(String name, int age, int score, int grade) {
super(name, age, score);
this.grade = grade;
}
public int getGrade() {
return this.grade;
}
public void setGrade(int grade) {
this.grade = grade;
}
}