Question

这是主要的课程

    **
** Assignment class
**
** This class represents an Assignment. 
**
****************************************************/
public class Assignment {
private String name;
private double pointsPossible;
private double pointsEarned;

 // Assignment constructor
 //
// postcondition: all instance variables are initialized with
// the given values. 
public Assignment (String n, double ptsPoss, double ptsEarned) {
 name =n;
pointsPossible=ptsPoss;
pointsEarned=ptsEarned;
 }
// getName accessor method
 //
 // postcondition: returns the name of this Assignment public 
String getName() {
return name;
    }

// getPointsPossible accessor method
//
// postcondition: returns the points possible for this Assignment
public double getPointsPossible() {
return pointsPossible;
    }
 // getPointsEarned accessor method
//
// postcondition: returns the points earned for this Assignment
public double getPointsEarned() {
return pointsEarned;
 }
}

当我尝试在我的子类中使用我的访问器时，我在尝试初始化其变量时遇到错误

这里是子类

import java.util.ArrayList;
/****************************************************
**
** CategoryAssignment class
**
** This class represents an CategoryAssignment. 
** Do not add any additional methods to this class.
**
****************************************************/
public class CategoryAssignment extends Assignment {
    // declare any new instance variables that you need here
    // don't forget to make them private!
    // don't declare more that you really need!
    // CategoryAssignment constructor
    //
    // postcondition: all instance variables are initialized with
    // the given values.     
    public CategoryAssignment (String n, double ptsPoss, double ptsEarned, String cat) {

    }

    // getCategoryName accessor method
    //
    // postcondition: returns the name of the category associated
    // with this CategoryAssignment
    public String getCategoryName() {
        return cat;
    }
}

我无法获取子类的变量来进行初始化。另外，这是一个成绩簿项目，将categories变量存储在数组或ArrayList中是否明智？

Answer 1

您的子类CategoryAssignment是否应该调用超类构造函数？类似的东西：

public CategoryAssignment (String n, double ptsPoss, double ptsEarned, String cat) {
    super(n, ptsPoss, ptsEarned);
    this.cat = cat;
}

您还需要在String cat中定义CategoryAssignment属性。

关于你的第二个问题＆＃34;另外，这是一个成绩簿项目，将categories变量存储在数组或ArrayList中是否明智？＆＃34;，就我在 getter ，cat变量是一个String。很难判断列表或数组是否最适合您提供的信息。

Answer 2

在Java中没有隐式构造函数链接这样的东西，即使子类＆＃39;和超类＆＃39;构造函数具有相同的签名。您需要将参数显式传递给超类＆＃39;带有super关键字的构造函数：

public CategoryAssignment
    (String n, double ptsPoss, double ptsEarned, String cat) {
    super(n, ptsPoss, ptsEarned, car);
}

Answer 3

首先：如果要访问此类，则必须在类中声明变量 cat 。您必须在课程中添加：

    private String cat;

下一步：子类'构造函数中的第一个语句是超类的构造函数。在你的情况下：

    public CategoryAssignment(String n, double ptsPoss, double ptsEarned, String cat) { 
       super(n, ptsPoss, ptsEarned);
       this.cat = cat; 
    }

子类的构造函数

3 个答案: