Java 子类有参构造器报错

Posted 2021-03-16 JessePeng

java

Java 子类的有参构造器报错：Implicit super constructor Person() is undefined. Must explicitly invoke another constructor

 

 

 

 

import java.util.*;

class Person {
    protected String firstName;
    protected String lastName;
    protected int idNumber;
    
    // Constructor
    Person(String firstName, String lastName, int identification){
        this.firstName = firstName;
        this.lastName = lastName;
        this.idNumber = identification;
    }
    
    // Print person data
    public void printPerson(){
         System.out.println(
                "Name: " + lastName + ", " + firstName 
            +     "\\nID: " + idNumber); 
    }
     
}

class Student extends Person{
    private int[] testScores;

    /*    
    *   Class Constructor
    *   
    *   @param firstName - A string denoting the Person\'s first name.
    *   @param lastName - A string denoting the Person\'s last name.
    *   @param id - An integer denoting the Person\'s ID number.
    *   @param scores - An array of integers denoting the Person\'s test scores.
    */
    // Write your constructor here
    Student(String firstName, String lastName, int id,  int[] scores){

　　　　　super()；   //隐藏会执行的默认构造器

        super(firstName, lastName, id);   //因为少了父类自定义构造器初始化，所以会报错
        
        this.firstName = firstName;
        this.lastName = lastName;
        this.idNumber = id;
        this.testScores = scores;
    }

    /*    
    *   Method Name: calculate
    *   @return A character denoting the grade.
    */
    // Write your method here
    public char calculate(){
        int num = testScores.length;
        int s = 0;
        for(int score : testScores) {
            s = s + score;
        }
        s = s/num;

        char grade = \'-\';
        if(s>=90&&s<=100){
            grade = \'O\';
        }else if(s>=80&&s<90){
            grade = \'E\';
        }else if(s>=70&&s<80){
            grade = \'A\';
        }else if(s>=55&&s<70){
            grade = \'P\';
        }else if(s>=40&&s<55){
            grade = \'D\';
        }else if(s<40){
            grade = \'T\';
        }
        return grade;
    }
}

class Solution {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String firstName = scan.next();
        String lastName = scan.next();
        int id = scan.nextInt();
        int numScores = scan.nextInt();
        int[] testScores = new int[numScores];
        for(int i = 0; i < numScores; i++){
            testScores[i] = scan.nextInt();
        }
        scan.close();
        
        Student s = new Student(firstName, lastName, id, testScores);
        s.printPerson();
        System.out.println("Grade: " + s.calculate());
    }
}

原因：父类的构造方法Person()只有有参数的构造方法，也可以说   父类没有无参的构造方法(即默认的super()初始化会报错) ，这样的话，子类继承该类，就必须要显示的调用父类的构造函数，这样才能保证，编译器在将子类初始化前，父类先被初始化。