Question

我试图找出Java中的继承和数组，我试图让这些类一起工作。我相信我有继承权，但我仍在努力与数组部分。

有三个文件：1。Person.java -base类2. Student.java-Person.java的派生类3. Family.java-不太确定，我认为它是自己的基类

Person.java有两个实例变量，String name和int age，以及各种构造函数，toString，equals和set / get方法

Student.java，同样是Person的派生类，根据定义，它将包含Person中包含的所有内容，以及另外两个实例变量，String major和double gpa。这个类还有major和gpa的get / set方法，一个equals方法，比较一个班级学生和另一个班级学生，我相信它被称为toString的重叠方法，返回name，age，major和gpa所有在一个字符串。

最后，Family.java是main方法所在的位置。它创建了一个Person类型的数组，添加＆＃34; Persons＆＃34;到这个数组，然后输出它们。

我收到的错误是：＆＃34; main＆＃34; java.lang.ArrayIndexOutOfBoundsException：8

我无法弄清楚为什么这个程序不能正常工作，并希望有任何帮助来解决这个问题。谢谢。

Person.java类

    public class Person 
{
private String name;
private int age;

public Person()
{
    name = "John Smith";
    age = 1;
}

public Person(String n, int a)
{
    name = n;
    age = a;
}

public String toString()
{
    return ("Name: " + getName() + ", Age: " + age + " ");
}

public boolean equals(Person otherPerson)
{
    return (getName().equals(otherPerson.getName()) && (age == otherPerson.age));
}

public String getName() 
{
    return name;
}

public void setName(String newName)
{
    name = newName;
}

public int getAge() 
{
    return age;
}

public void setAge(int newAge)
{
    age = newAge;
}

}

Student.java类

public class Student extends Person
{
private String major;
private double gpa;

public Student()
{
    super();
    major = "Undecided";
    gpa = 0.0;
}

public Student(String theName, int theAge, String theMajor, double theGpa)
{
    super(theName, theAge);
    setMajor(theMajor);
    setGpa(theGpa);
}

public String toString()
{
    return ("Name: " + getName() + ", Age: " + getAge() + ", Major: " + major + ", GPA: " + gpa);
}

public boolean equals(Student otherStudent)
{
    return (major.equals(otherStudent.major) && (gpa == otherStudent.gpa));
}

public String getMajor() 
{
    return major;
}

public void setMajor(String newMajor)
{
    major = newMajor;
}

public double getGpa() 
{
    return gpa;
}

public void setGpa(double newGpa)
{
    gpa = newGpa;
}

}

Family.java类

public class Family
{
private int famArray = 0;
private Person[] family;

public Family(int size_of_family)
{
    famArray = size_of_family;
    family = new Person[famArray];
}   
public void addPerson(Person p)
{
    boolean isPresent = false;

    int i;
    for(i = 0; i < family.length; i++)
    {

        if(family[i] != null && family[i].equals(p))
        {
            isPresent = true;
            System.out.println(p.getName() + 
            " is already present in the family");
        }                       
    }      
    if(isPresent == false)
        family[i] = p;
}
public void printOutFamily()
{
    for(int i = 0; i < family.length; i++)
    {
        System.out.println(family[i].toString());
    }
}
public static void main(String[] args)
{
    Family f = new Family(8);
    Person fred= new Person("Fred Flintstone", 50);
    System.out.println("created " + fred);
    f.addPerson(fred);
    f.addPerson(fred);

    Student fredStudent = new Student("Fred Flintstone", 50, "Math", 3.1);
    System.out.println("created "+ fredStudent);
    f.addPerson(fredStudent);

    Person wilma = new Person("Wilma Flintstone", 48);
    f.addPerson(wilma);


    Student george= new Student("George", 21, "Politics", 3.1);
    System.out.println("created " + george);
    f.addPerson(george);

    george.setName("Georgie");
    f.addPerson(new Student("George", 21, "Politics", 3.1));



    f.addPerson(new Student("John", 18, "Geology", 2.9));
    f.addPerson(new Student("Jane", 21, "Music", 3.2));
    f.addPerson(new Student("Tarzan", 22, "Gymnastics", 4.0));
    f.addPerson(new Student("Jim", 21, "Physics", 2.5));


    System.out.println("****** family listing: ");
    f.printOutFamily();

}
}

Answer 1

问题在于Family#addPerson方法：

if(isPresent == false)
    family[i] = p;

您正在添加位置i中的元素。如果找不到该元素，则i值将为family.length，从而为您提供例外。

改为使用int famArray字段：

if(isPresent == false) {
    family[famArray++] = p;
}

或者以更简单的方式为初学者提供：

if(isPresent == false) {
    family[famArray] = p;
    famArray = famArray + 1;
}

作为当前问题的补充，您应首先检查famArray元素是否等于family.length。如果它们相同，则增加数组或不允许更多元素。

你说你有同样的问题。这是因为您使用famArray类构造函数中指出的数组长度初始化Family：

public Family(int size_of_family) {
    famArray = size_of_family; //here
    family = new Person[famArray];
}

将代码更改为：

public Family(int size_of_family) {
    famArray = 0;
    family = new Person[size_of_family];
}

你已经完成了。

Answer 2

问题在于

行

family[i] = p;

这发生在for循环之后，它使i增加到等于数组的长度。我没有任何修改建议，因为我不确定你在这里做什么。

类的Java继承

2 个答案: