我要创建一个Java控制台应用程序,该应用程序定义一个类,将其扩展为其他两个类,为所有三个类覆盖toString(),将这些类实例化为三个对象,并在这些对象上调用toString(),打印出每个toString()调用的返回值。
应用程序将实例化Course,FlexPathCourse和GuidedPathCourse中的三个对象,并调用它们对应的toString()方法。
我有以下代码。但是对于FlexPathCourse.java和GuidedPathCourse.java,我在“ super(code1,hours,title1)”所在的位置收到一条错误消息“类对象中的构造方法对象无法应用于给定类型”。您能解释一下这意味着什么,我应该做什么吗?预先谢谢你。
Main Class
public class U1A1_InheritOverridetoString {
public static void main(String[] args) {
Course c1 = new Course("TBD", 3, "TBD");
FlexPathCourse c2 = new FlexPathCourse("IT2230", 3, "Introduction to Database Systems");
GuidedPathCourse c3 = new GuidedPathCourse("ITFP4739", 3, "Mobile Cloud Computing Application Development");
System.out.println(c1);
System.out.println(c2);
System.out.println(c3);
}
}
Course.java
public class Course {
protected String code;
protected int creditHours;
protected String title;
public Course(String code1, int hours, String title1){
code = code1;
creditHours = hours;
title = title1;
}
@Override
public String toString(){
return "Java class name = 'Course' " + "Course Code = " + code;
}
}
FlexPathCourse.java
public class FlexPathCourse {
private String optionalResources;
public FlexPathCourse (String code1, int hours, String title1){
super(code1, hours, title1);
}
@Override
public String toString(){
return "Java class name = 'FlexPathCourse' " + "Course Code = " + code;
}
}
GuidedPathCourse.java
public class GuidedPathCourse {
private String requiredResources;
private int duration;
public GuidedPathCourse(String code1, int hours, String title1){
super(code1, hours, title1);
}
@Override
public String toString(){
return "Java class name = 'GuidedPathCourse' " + "Course Code = " + code;
}
}
答案 0 :(得分:1)
好像您错过了扩展课程一样,
public class FlexPathCourse extends Course
或
public class GuidedPathCourse extends Course
答案 1 :(得分:1)
Super引用了它扩展的类。
[SuperClass] -> [class]
就您而言
[Course] -> [FlexPathCourse]
-> [GuidedPathCourse]
为了告诉有关这种关系(继承)的Java,您需要使用extends
,例如:public class FlexPathCourse extends Course { ... }
之后,您可以使用继承属性,例如多态性,这是Java中的重要功能。
此链接中的解释:https://www.w3schools.com/java/java_polymorphism.asp
Constructor object in class object cannot be applied to given types
意味着您没有这样声明构造函数,扩展类时将解决此问题,因为现在它可以识别您在Course类中声明的super()构造函数
答案 2 :(得分:1)
如果要扩展一个类,则在声明另一个类时应使用extend
public class GuidedPathCourse extends Course{
private String requiredResources;
private int duration;
public GuidedPathCourse(String code1, int hours, String title1){
super(code1, hours, title1);
}
@Override
public String toString(){
return "Java class name = 'GuidedPathCourse' " + "Course Code = " + code;
}
}
与FlexPathCourse相同
答案 3 :(得分:0)
像这样添加extends Course
:
public class GuidedPathCourse extends Course {