Java 添加方法链接列表

我已经创建了一个包含对象的链表。该对象称为Student，有三个参数：姓名、年龄、年级。这是我的课

链接

class Link {
    public Object s;
    public Link next;

    public Link(Object Student) {
        s=Student;
        next=null;
    }
}

学生

class Student {
    private static String name;
    private static int age;
    private static int grade;

    public Student (String n, int a, int g) {
        setName(n);
        setGrade(g);
        setAge(a);
    }

    public static void setName(String n) {
        name=n;
    }

    public static void setGrade(int g) {
        grade=g;
    }

    public static void setAge(int a) {
        age=a;
    }

    public int getAge() {
        return age;
    }

    public int getGrade() {
        return grade; 
    }

    public static String getName() {
        return name;
    }

    public String toString() {
        return "Name: " +name+ " Age: " +age+ " Grade: " +grade; 
    }
}

import java.util.*;
class List {
    private static LinkedList<Student> ll = new LinkedList<Student>();
    private static Link first;
    public List() {
        first=null;
    }

    public static void addStudent() {
        Scanner s = new Scanner(System.in);
        System.out.println("What is the student's name;");
        String n = s.nextLine();
        System.out.println("What is the student's age;");
        int b = s.nextInt();
        System.out.println("What is the student's grade;");
        int g = s.nextInt();
        Student nStudent = new Student(n, b, g);
        Link newStudent = new Link(nStudent);
        newStudent.next=first;
        first=newStudent;
        ll.add(nStudent);
    }

    public static Link findStudent() {
        Scanner sc = new Scanner(System.in);
        System.out.println("What is the student's name?");
        String n = sc.nextLine();
        Link current = first;
        String name = Student.getName();
        while (name!= n) {
            if (current.next==null)
                return null;
            else
                current=current.next;
        }
        return current;
    }

    public static void change () {
        Scanner sc = new Scanner(System.in);
        Link h = findStudent();
        System.out.println("If you want to change his name press 1;");
        System.out.println("If you want to change his age press 2;");
        System.out.println("If you want to change his grade press 3;");
        int l = sc.nextInt();
        if (l==1) {
            System.out.println("What name do you want the student to have?");
            String newname = sc.nextLine();
            Student.setName(newname);

        } else if (l==2) {
            System.out.println("What age do you want the student to have?");
            int j = sc.nextInt();
            Student.setAge(j);
        }
        else if (l==3) {
            System.out.println("What grade do you want the student to have?");
            int e = sc.nextInt();
            Student.setGrade(e);
        }
    }

    public static void show() {
        System.out.println(ll);
    }
}

What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3
1
What is the student's name;
Tom
What is the student's age;
16
What is the student's grade;
90
What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3
1
What is the student's name;
Eric
What is the student's age;
16
What is the student's grade;
91
What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3
3
[Name: Eric Age: 16 Grade: 91, Name: Eric Age: 16 Grade: 91]
What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3

列表

class Student {
    private static String name;
    private static int age;
    private static int grade;

    public Student (String n, int a, int g) {
        setName(n);
        setGrade(g);
        setAge(a);
    }

    public static void setName(String n) {
        name=n;
    }

    public static void setGrade(int g) {
        grade=g;
    }

    public static void setAge(int a) {
        age=a;
    }

    public int getAge() {
        return age;
    }

    public int getGrade() {
        return grade; 
    }

    public static String getName() {
        return name;
    }

    public String toString() {
        return "Name: " +name+ " Age: " +age+ " Grade: " +grade; 
    }
}

import java.util.*;
class List {
    private static LinkedList<Student> ll = new LinkedList<Student>();
    private static Link first;
    public List() {
        first=null;
    }

    public static void addStudent() {
        Scanner s = new Scanner(System.in);
        System.out.println("What is the student's name;");
        String n = s.nextLine();
        System.out.println("What is the student's age;");
        int b = s.nextInt();
        System.out.println("What is the student's grade;");
        int g = s.nextInt();
        Student nStudent = new Student(n, b, g);
        Link newStudent = new Link(nStudent);
        newStudent.next=first;
        first=newStudent;
        ll.add(nStudent);
    }

    public static Link findStudent() {
        Scanner sc = new Scanner(System.in);
        System.out.println("What is the student's name?");
        String n = sc.nextLine();
        Link current = first;
        String name = Student.getName();
        while (name!= n) {
            if (current.next==null)
                return null;
            else
                current=current.next;
        }
        return current;
    }

    public static void change () {
        Scanner sc = new Scanner(System.in);
        Link h = findStudent();
        System.out.println("If you want to change his name press 1;");
        System.out.println("If you want to change his age press 2;");
        System.out.println("If you want to change his grade press 3;");
        int l = sc.nextInt();
        if (l==1) {
            System.out.println("What name do you want the student to have?");
            String newname = sc.nextLine();
            Student.setName(newname);

        } else if (l==2) {
            System.out.println("What age do you want the student to have?");
            int j = sc.nextInt();
            Student.setAge(j);
        }
        else if (l==3) {
            System.out.println("What grade do you want the student to have?");
            int e = sc.nextInt();
            Student.setGrade(e);
        }
    }

    public static void show() {
        System.out.println(ll);
    }
}

What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3
1
What is the student's name;
Tom
What is the student's age;
16
What is the student's grade;
90
What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3
1
What is the student's name;
Eric
What is the student's age;
16
What is the student's grade;
91
What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3
3
[Name: Eric Age: 16 Grade: 91, Name: Eric Age: 16 Grade: 91]
What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3

您会注意到，在课程中，我多次编写相同的代码，但这是因为我无法找到一种方法，在执行命令后，我可以返回主菜单，并且列表的内容不会丢失。 显然，我的add方法是错误的，当我执行程序时，输出如下：

输出

class Student {
    private static String name;
    private static int age;
    private static int grade;

    public Student (String n, int a, int g) {
        setName(n);
        setGrade(g);
        setAge(a);
    }

    public static void setName(String n) {
        name=n;
    }

    public static void setGrade(int g) {
        grade=g;
    }

    public static void setAge(int a) {
        age=a;
    }

    public int getAge() {
        return age;
    }

    public int getGrade() {
        return grade; 
    }

    public static String getName() {
        return name;
    }

    public String toString() {
        return "Name: " +name+ " Age: " +age+ " Grade: " +grade; 
    }
}

import java.util.*;
class List {
    private static LinkedList<Student> ll = new LinkedList<Student>();
    private static Link first;
    public List() {
        first=null;
    }

    public static void addStudent() {
        Scanner s = new Scanner(System.in);
        System.out.println("What is the student's name;");
        String n = s.nextLine();
        System.out.println("What is the student's age;");
        int b = s.nextInt();
        System.out.println("What is the student's grade;");
        int g = s.nextInt();
        Student nStudent = new Student(n, b, g);
        Link newStudent = new Link(nStudent);
        newStudent.next=first;
        first=newStudent;
        ll.add(nStudent);
    }

    public static Link findStudent() {
        Scanner sc = new Scanner(System.in);
        System.out.println("What is the student's name?");
        String n = sc.nextLine();
        Link current = first;
        String name = Student.getName();
        while (name!= n) {
            if (current.next==null)
                return null;
            else
                current=current.next;
        }
        return current;
    }

    public static void change () {
        Scanner sc = new Scanner(System.in);
        Link h = findStudent();
        System.out.println("If you want to change his name press 1;");
        System.out.println("If you want to change his age press 2;");
        System.out.println("If you want to change his grade press 3;");
        int l = sc.nextInt();
        if (l==1) {
            System.out.println("What name do you want the student to have?");
            String newname = sc.nextLine();
            Student.setName(newname);

        } else if (l==2) {
            System.out.println("What age do you want the student to have?");
            int j = sc.nextInt();
            Student.setAge(j);
        }
        else if (l==3) {
            System.out.println("What grade do you want the student to have?");
            int e = sc.nextInt();
            Student.setGrade(e);
        }
    }

    public static void show() {
        System.out.println(ll);
    }
}

What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3
1
What is the student's name;
Tom
What is the student's age;
16
What is the student's grade;
90
What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3
1
What is the student's name;
Eric
What is the student's age;
16
What is the student's grade;
91
What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3
3
[Name: Eric Age: 16 Grade: 91, Name: Eric Age: 16 Grade: 91]
What do you want to do?
To add a student press 1
To change something press 2
To see your students press 3

---

为什么我在类中添加一个学生时，它是重复的？

我认为你的问题是，你的Student.class是静态的

private static String name;
private static int age;
private static int grade;

这一部分告诉java，您只需要一个变量/类。因此，您的链表只存储对相同静态字段的2个引用

---

您需要删除static关键字。

因为您在学生课堂上使用的是静态字段

private static String name;
private static int age;
private static int grade;

静态字段不属于实例，而是属于类本身。 无论您创建了多少个学生实例（使用

new

关键字），

static

字段的值将在他们之间共享

您必须删除学生类中的

static

关键字。

---

请参阅官方文档：

所有问题都是由于您决定在

学生

课堂上使用

静态

变量造成的。这意味着，无论您创建了多少

Student

对象，整个类中每个变量只有一个副本

使它们非静态。这意味着您必须在

Student

类中删除

static

的getter和setter

在

列表

类中，可以从静态上下文访问getter，例如

Student.getName（）

。您需要将对象存储在

链接中

并将其强制转换为

学生

。然后，您将能够对其调用

getName（）

另一方面，

链接

类应该是一个泛型类，例如

类链接

，这样当您在

列表

类中使用它时，您可以将其用作

链接

，因此在引用它所持有的

对象时不必强制转换它（它将持有一个
t
）

在
change
中，您将需要执行类似的操作--对于
findStudent
找到的
Student
引用的
Student，调用该Student对象上的setter，而不是在静态上下文中调用它

此外，在
中查找学生
，而不是
=
或
==
但是如果我删除静态引用，我会有其他多个错误。不用担心，IDE正在帮助您。您还必须从setter/getter函数中删除静态限定符。例如：publicstaticvoidsetgrade这很重要，你要理解static的真正含义，慢慢来。但是如果我删除静态引用，我会出现错误，比如：非静态方法可以引用静态内容你必须从getter和setter中删除static关键字。这是因为您无法从静态方法访问非静态字段。如果您有兴趣了解更多关于static关键字的信息，可以参考以下文档：如何修复change方法中的bug？