java - 如何将对象添加到链表中？

Question

我一直在做一个项目，我必须实现一个 java 类来实现双向链表的使用。我用我所有的方法完成了 LinkedList 类。我只是不确定如何将节点对象实际添加到列表中。到目前为止，这是我的代码，底部有测试。任何帮助，将不胜感激。谢谢

public class LinkedList {

    private Node first;
    private Node current;
    private Node last;
    private int currentIndex;
    private int numElements;

    public LinkedList() {
        this.first = null;
        this.last = null;
        this.numElements = 0;
        this.current = null;
        this.currentIndex = -1;
    }

    private class Node {

        Node next;
        Node previous;
        Object data;
    }

    public boolean hasNext() {
        return (current != null && current.next != null);
    }

    public Object next() {
        if (!this.hasNext()) {
            throw new IllegalStateException("No next");
        }

        current = current.next;
        return current.data;

    }

    public boolean hasPrevious() {
        return (current != null && current.previous != null);

    }

    public Object previous() {
        if (!this.hasPrevious()) {
            throw new IllegalStateException("No previous");
        }
        current = current.previous;
        return current.data;

    }

   int nextIndex() {
        int index = numElements;
        if (hasNext()) {
            index = this.currentIndex + 1;
        }
        System.out.println(index + "The current index is " + current);
        return index;
    }

    int previousIndex() {
        int index = -1;
        if (hasPrevious()) {
            index = this.currentIndex - 1;
        }
        System.out.println(index + "The current index is " + current);
        return index;
    }

    public void set(Object o) {
        if (this.current == null) {
            throw new IllegalStateException("No node found, cannot set.");
        }
        current.data = o;
    }

    public int size() {
        return numElements;
    }

    public void add(Object o) {       
        Node newNode = new Node();
        newNode.data = o;
        if (first == null) {
            first = newNode;
            last = newNode;
            newNode.next = null;

        } else if (first != null) {
            if (current == null) {
                newNode.previous = null;
                newNode.next = first;
                first.previous = newNode;
                first = newNode;
            } else if (current == last) {
                newNode.previous = current;
                newNode.next = null;
                current.next = newNode;
                last = newNode;
            } else {
                newNode.previous = current;
                newNode.next = current.next;
                current.next.previous = newNode;
                current.next = newNode;
            }
        }
        current = newNode;
        numElements++;
        currentIndex++;

    }

    public void remove() {
        if (current != null) {
            if (current == first && current == last) {
                first = null;
                last = null;
            } else if (current == last) {
                current.previous = null;
                last = current.previous;
            } else if (current == last) {
                current.previous.next = null;
                last = current.previous;
            } else {
                current.previous.next = current.next;
                current.next.previous = current.previous;
            }
            current = current.next;
            numElements--;
        }
    }
}



import java.util.Scanner;


public class LinkedListTest {
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        String name;
        int index;

        LinkedList<Object> listOne = new LinkedList<Object>();

        listOne.add(object o);

    }
}

score 4 · Accepted Answer

发布的类 LinkedList 对我来说看起来很实用。

确保您的测试代码不会混淆java.util.LinkedListJava 为您提供的此类和（它是现有 Collections 框架的一部分）。

为清楚起见，我建议将您的课程重命名为MyLinkedList

以下代码有效，输出为“0”，“2”：

public class MyLinkedListTest {

    public static final void main(String[] args) {

        MyLinkedList list = new MyLinkedList();
        System.out.println("Number of items in the list: " + list.size());

        String item1 = "foo";
        String item2 = "bar";

        list.add(item1);
        list.add(item2);

        System.out.println("Number of items in the list: " + list.size());      

        // and so on...
    }

}

score 2 · Accepted Answer

如果您的代码已编译，我会感到惊讶，因为您的类实际上不是通用的。只需将其初始化为LinkedList listOne = new LinkedList();（无尖括号）。

至于实际添加元素，您只需要添加一些的实例Object即可；任何事情都会做（假设您的内部代码正常工作）。在最后尝试一下：

Object objectToAdd = "Strings are Objects";
listOne.add(objectToAdd);
objectToAdd = new File("C:\\foo.bar"); // Or use any other Objects!
listOne.add(objectToAdd);

score 1 · Accepted Answer

您LinkedList没有泛型类型，因此您不能将其声明为

LinkedList<Object> listOne = new LinkedList<Object>();

而是作为

LinkedList listOne = new LinkedList();

现在添加元素只需使用您的add方法

listOne.add("something");
listOne.add(1);//int will be autoboxed to Integer objects

此外，如果您想从键盘添加数据，您可以使用类似

String line="";
do{
    System.out.println("type what you want to add to list:");
    line = keyboard.nextLine();
    listOne.add(line);
}while(!line.equals("exit"));

score 1 · Accepted Answer

考虑编号列表并查看元素之间的关系

说我有清单：

一个
乙
C

我必须对关系做什么才能得到列表：

一个
乙
新节点
C

B的新下一个节点是NewNode C的新的前一个节点是NewNode。因此，插入函数会想知道紧邻的前一个节点或紧邻的下一个节点，然后调整关系。

score 0 · Accepted Answer

线

LinkedList<Object> listOne = new LinkedList<Object>();

除非您将类声明更改为

class LinkedList<T>

或者你也可以写

LinkedList listOne = new LinkedLis();

之后，您应该能够将对象添加到列表中。但是，您需要创建一个对象来添加到它，listOne.add(object o);不会这样做 - 至少您必须编写listOne.add(new Object()). （您的代码没有实例化 Object，没有您已经调用过的 Object，o此外，object o在 Java 中没有任何意义，也不会编译。

score 0 · Accepted Answer

正如人们所提到的，您的列表并不通用。但是，由于他们建议您摆脱该参数，您也可以将<Object>或添加<E>到您的链表实现中，并保持列表的初始化不变。

因此，在您的链表类中，您应该执行以下操作：

public class LinkedList<E>

这将确保您在使用时LinkedList<Object> listOne = new LinkedList<Object>();，E将被确认为Object

score 0 · Accepted Answer

让我们稍微改进一下您的测试，以便您的问题出在哪里（如果有的话）我注释掉了对 current() 方法的调用，因为您没有包含一个。（我会不理会它，因为它可能会让您感到困惑。）一般的想法是将项目添加到链接列表中，并在它中前后移动，检查每一步的项目。

public class LinkedListTest {
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        String name;
        int index;

        LinkedList listOne = new LinkedList();
        //Initially we should be empty so we are positioned
        // at both the beginning and end of the list
        assert listOne.size() == 0 :"List should be empty";
        assert listOne.hasPrevious()==false: "Should be at the beginning of the list";
        assert listOne.hasNext()==false : "Should be at the end of the list";

        Object firstNode = "I am the first node";
        listOne.add(firstNode); //we've added something
//I left this commented out since you don't have a current() method.
//        assert firstNode == listOne.current() : "Our current item should be what we just added";
        assert listOne.hasPrevious()==false : "Should not have moved forward in our list yet";
        assert listOne.hasNext()==true : "should have an item after our current";
        assert listOne.size() == 1 : "Should only have one item in the list";
        Object secondNode = "I am the second node";
        listOne.add(secondNode);
        assert listOne.size() == 2 : "Should only have two items in the list";

        assert firstNode == listOne.next() : "1st call to next should return the 1st node";
        assert listOne.hasPrevious()==true : "We should be positioned after the 1st node";
        assert listOne.hasNext()==true : "We should be positioned before the 2nd node";
    }
}

java - 如何将对象添加到链表中？

7 回答 7

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