在Java中如何在排序列表中插入元素
我必须用java创建自己的列表。要插入的元素(Person元素)必须进行排序(从低到高)。 因此,我创建了一个方法compareTo来检查插入人员的姓名。 问题在于插入方法。我写了这段代码:在Java中如何在排序列表中插入元素,java,list,class,sorting,insert,Java,List,Class,Sorting,Insert,我必须用java创建自己的列表。要插入的元素(Person元素)必须进行排序(从低到高)。 因此,我创建了一个方法compareTo来检查插入人员的姓名。 问题在于插入方法。我写了这段代码: public boolean insert(Person p){ PersonListElement element = new PersonListElement(p); boolean inserted = false; if(containsElement(p) == true
public boolean insert(Person p){
PersonListElement element = new PersonListElement(p);
boolean inserted = false;
if(containsElement(p) == true){
inserted = false;
return inserted;
}
if(head == null){
head = element;
size = size + 1;
inserted = true;
return inserted;
}
PersonListElement position = head;
PersonListElement prev = null;
while(position != null){
if(position.getValue().compareTo(element.getValue()) < 0){
if(prev != null){
prev.setNext(element);
element.setNext(position);
inserted = true;
position = null;
}
prev = position;
position = position.getNext(); //here i get pointerException prob.
}
}
if(inserted == false && prev != null){
prev.setNext(element);
inserted = true;
}
size = size + 1;
return inserted;
}
通过这个类,我测试了我的代码:
class SortList
{
public static void main(String args[]){
SortedList list = new SortedList();
Person a = new Person("Alice", 10);
list.insert(a);
a = new Person("Al", 20);
list.insert(a);
a = new Person("Bo", 90);
list.insert(a);
p = new Person("Cin", 3);
list.insert(a);
System.out.println(list);
}
}
您需要完成迭代和插入。假设您正在实现一个链表,并且在
liselement
类中有一个publicnext
属性
public boolean insert(Person p){
ListElement element = new StackElement(p);
boolean inserted = false;
if(head == null){
head = element;
size = size + 1;
inserted = true;
return inserted;
}
ListElement temp = head;
ListElement prev = null;
while(temp != null){
if(temp.compareTo(element) < 0) {
if(prev != null) prev.next = element; //Keep the chain connected
element.next = temp; //Insert you element before temp
inserted = true;
break;
}
prev = temp;
temp = temp.next;
}
}
if(!inserted && temp == null && prev != null) { //You may want to insert it at the end of the list if no upper element is found.
prev.next = element; //Put it at the end.
inserted = true;
}
if(inserted) size = size + 1;
return inserted; //This should be true in any case but I left it for the case you want to avoid inserting the element at the end if its place is not found.
}
关于你的delete
方法,我认为你把事情弄得太复杂了。
在迭代中,您只需要保留两个引用:一个用于前一个元素,另一个用于当前元素。
如果您的第一个元素是要删除的元素,则您的prev
引用将为null
,并且您必须更新头
。否则,您需要更新prev
next reference,使其引用当前之后的元素:
public boolean delete(Person p){
boolean deleted = false;
PersonListElement current = head;
PersonListElement prev = null;
while(current != null && !deleted){
if(current.getValue().compareTo(p) == 0){
if(prev != null)
prev.setNext(current.getNext());
else
head = current.getNext();
deleted = true;
} else {
prev = current;
current = current.getNext();
}
}
if(deleted) size--;
return deleted;
}
你的类的其余部分看起来是什么样子的?不确定你的赋值是否允许,但是Java有一些很好的排序功能,使用你的compareTo方法,你已经完成了一半。我无法理解下面的代码:if(prev!=null)prev.next=element//保持链条连接元件。下一步=温度//在temp inserted=true之前插入元素;temp=null;}prev=温度;温度=下一个温度;您能帮助我吗?@usersuperprev
在temp
之前保留对节点的引用。您要询问的if
语句用于检查是否存在前一个元素,在这种情况下,您必须将元素放在它的正后方(通过使其属性next
引用element
),并且在任何情况下都要放在temp
之前(通过制作元素。下一步参考temp
).现在更清楚了吗?我接受了你的答案。我还有一个关于删除元素的问题。我试图做到这一点,但我认为如果元素位于列表的末尾,我的代码就不起作用了。我的代码如下。我删除了我的答案。如果我想删除最后一个元素,我不确定你的删除方法是否有效,因为if(prev!=null){prev.setNext(current.getNext());}。那么我认为这可能有问题,因为current.getNext()不存在
public void insert(Person p){
ListElement element = new StackElement(p);
if(head == null){
head = element;
size = size + 1;
return;
}
ListElement temp = head;
ListElement prev = null;
boolean inserted = false;
while(temp != null){
if(temp.compareTo(element) < 0) {
if(prev != null) prev.next = element; //Keep the chain connected
element.next = temp; //Insert you element before temp
inserted = true;
temp = null;
} else {
prev = temp;
temp = temp.next;
}
}
}
if(!inserted && prev != null)
{
prev.next = element; //Put it at the end.
}
size = size + 1;
}
public boolean delete(Person p){
boolean deleted = false;
PersonListElement current = head;
PersonListElement prev = null;
while(current != null && !deleted){
if(current.getValue().compareTo(p) == 0){
if(prev != null)
prev.setNext(current.getNext());
else
head = current.getNext();
deleted = true;
} else {
prev = current;
current = current.getNext();
}
}
if(deleted) size--;
return deleted;
}