链表的查找解决方法

链表的查找

Java code

package ShuJuJieGou.Ch05;/** * * 双端链表 */class Link4 {    public long dData;    public Link4 next;    public Link4(long d) {        dData = d;    }    public void displayLink() {        System.out.print(dData + " ");    }}class FirstLastList {    private Link4 first;    private Link4 last;    public FirstLastList() {        first = null;        last = null;    }    public boolean isEmpty() {        return first == null;    }    public void insertFirst(long dd) {        Link4 newlink = new Link4(dd);        if (isEmpty()) {            last = newlink;        }        newlink.next = first;        first = newlink;    }    //first 和 last 是同一个对象，每次插入后，last都指向最后一个值    public void insertlast(long dd) {        Link4 newlink = new Link4(dd);        if (isEmpty()) {            first = newlink;        } else {            last.next = newlink;        }        last = newlink;    }    public long deleteFirst() {        long temp = first.dData;        if (first.next == null) {            last = null;        }        first = first.next;        return temp;    }    //查找方法    public Link4 find(long d) {        Link4 temp = first;        while (first.dData != d) {            if (temp == null) {                return null;            }else{            temp = temp.next;            }        }        return temp;    }    //删除    public Link4 delete(long d) {        Link4 persous = first;        Link4 current = first;        while (current.dData != d) {            if (current == null) {                return null;            } else {                persous = current;                current = current.next;            }        }        if (current == first) {            first = first.next;        } else {            persous.next = current.next;        }        return current;    }    public void displayList() {        System.out.print("List(first-->last):");        Link4 current = first;        while (current != null) {            current.displayLink();            current = current.next;        }        System.out.println("");    }}public class Test4 {    public static void main(String[] args) {        FirstLastList thelist = new FirstLastList();        thelist.insertFirst(22);        thelist.insertFirst(44);        thelist.insertFirst(66);        thelist.insertFirst(88);        thelist.insertlast(11);        thelist.insertlast(33);        thelist.insertlast(55);        thelist.displayList();        thelist.deleteFirst();        thelist.deleteFirst();        thelist.displayList();        //测试删除        thelist.delete(11);        thelist.displayList();        //测试查找                                                错误在这里，我在一个单链表使用这个查找功能正常使用，而在双端链表却不行        Link4 temp=thelist.find(22);        temp.displayLink();    }}

Java code

 public Link4 find(long d) {        Link4 temp = first;        while (first.dData != d) {            if (temp == null) {                return null;            }else{            temp = temp.next;//这里temp.next是不是为null            }        }        return temp;    }
[解决办法]
Java code
 
 class Link4 { 
  
   public long dData; 
   public Link4 next; 
  
   public Link4(long d) { 
     dData = d; 
   } 
  
   public void displayLink() { 
    
     System.out.print(dData + " "); 
   } 
 } 
  
 class FirstLastList { 
  
   private Link4 first; 
   private Link4 last; 
  
   public FirstLastList() {  
 
     first = null; 
     last = null; 
   } 
  
   public boolean isEmpty() { 
     return first == null; 
   } 
  
   public void insertFirst(long dd) { 
     Link4 newlink = new Link4(dd); 
  
     if (isEmpty()) { 
       last = newlink; 
     } 
     newlink.next = first; 
     first = newlink; 
   } 
  
   //first 和 last 是同一个对象，每次插入后，last都指向最后一个值 
   public void insertlast(long dd) { 
     Link4 newlink = new Link4(dd); 
     if (isEmpty()) { 
       first = newlink; 
     } else { 
       last.next = newlink; 
     } 
     last = newlink; 
   } 
  
   public long deleteFirst() { 
     long temp = first.dData; 
     if (first.next == null) { 
       last = null; 
     } 
     first = first.next; 
     return temp; 
   } 
  
   //查找方法 
   public Link4 find(long d) { 
     Link4 temp = first; 
     while (temp.dData != d) { 
       if (temp == null) { 
         return null; 
       }else{ 
       temp = temp.next; 
       if(temp == null) {//这样改就ＯＫ了 
       return null; 
       } 
  
       } 
     } 
     return temp; 
   } 
  
   //删除 
   public Link4 delete(long d) { 
     Link4 persous = first; 
     Link4 current = first; 
     while (current.dData != d) { 
  
       if (current == null) { 
         return null; 
       } else { 
         persous = current; 
         current = current.next; 
       } 
     } 
     if (current == first) { 
       first = first.next; 
     } else { 
       persous.next = current.next; 
     } 
     return current; 
   } 
  
   public void displayList() { 
     System.out.print("List(first-->last):"); 
     Link4 current = first; 
      
     while (current != null) { 
       current.displayLink(); 
       current = current.next; 
     } 
     System.out.println(""); 
   } 
 } 
  
 public class Test4 { 
  
   public static void main(String[] args) { 
     FirstLastList thelist = new FirstLastList(); 
  
     thelist.insertFirst(22); 
     thelist.insertFirst(44); 
     thelist.insertFirst(66); 
     thelist.insertFirst(88); 
  
     thelist.insertlast(11); 
     thelist.insertlast(33); 
     thelist.insertlast(55); 
  
     thelist.displayList(); 
  
     thelist.deleteFirst(); 
     thelist.deleteFirst(); 
     thelist.displayList(); 
  
  
     //测试删除 
     thelist.delete(11); 
     thelist.displayList(); 
  
     //测试查找                        错误在这里，我在一个单链表使用这个查找功能正常使用，而在双端链表却不行 
     Link4 temp=thelist.find(66); 
     if(temp == null) { 
     System.out.println("没有这个数！");  
 
     }else{ 
     temp.displayLink(); 
     } 
   } 
 } 
  
  
  

[解决办法]
查找方法跟main函数的错误差不多，都需要判断temp是否为null
在main函数最后要判断一下temp要是为null的话就不能引用temp.dＤata，否则会引发异常