为什么LinkedList的removeAll（）和removeFirstOccurrence（）删除节点？

Question

我必须编写这些方法的代码。这是一项家庭作业，不能改变方法的参数，或者写其他方法。 contains（）和isEmpty（）正常工作。 removeFirst（）和removerLast（）也可以很好地工作。

removeFirstOccurence（）不会删除指定元素的第一个成员。 而removeAll（）不会取消所有指定的元素。

/** 
* Removes the first occurrence of the specified element in this list (when 
* traversing the list from head to tail). * 
* @param value element to be removed from this list, if present 
* @return {@code true} if the list contained the specified element 
*/ 
public boolean removeFirstOccurrence(int value) { 
    if(!contains(value)) 
     return false; 
    else{ 
     boolean result = false; 
     Node current = head; 
     while ((current != null) && !result) { 
      if (current.value == value){ 
       current=current.next; 
       size--; 
       return true; 
       } 
      current = current.next; 
     } 
     return result; 
    } 
} 
/** 
* Removes all occurrences of the specified element from this list. 
* @param value the element to remove 
* @return {@code false} if nothing changed, otherwise {@code true} 
*/ 
public boolean removeAll(int value) { 
    if(isEmpty()) 
     return false; 
    else{ 
     boolean result = false; 
     Node current = head; 
     while ((current.next != null) && !result) { 
      if (current.value == value){ 
       current=current.next; 
       size--; 
       result=true; 
      }     
      current= current.next; 
     } 
     return result; 
    } 
} 

这里MyLinkedList类的第一部分：

public class MyLinkedList { 

private class Node { 

    private int value; 
    private Node next; 

    private Node(int value) { 
     this.value = value; 
     this.next = null; 
    } 

    @Override 
    public String toString() { 
     ... 
    } 
} 

private Node head; 
private int size; 

//和方法...

Answer 1

你永远不会改变任何节点以任何方式

public boolean removeFirstOccurrence(int value) { 
    //don't do contains(), you are looping over the entire thing anyway doing it again is useless 
    if(head==null)return false; 
    if(head.value==value){//does head contain the value 
     head=head.next; 
     size--; 
     return true; 
    } 
    Node prev = head; 
    while ((prev.next != null)) {//actually checking prev.next if it contains the value 
     if (prev.next.value == value){ 
      prev.next=prev.next.next; //remove link from prev to prev.next 
      size--; 
      return true; 
     } 
     prev = prev.next; 
    } 
    return false; 
} 

public boolean removeAll(int value) { 
    if(head==null)return false; 
    while(head.value==value){//does head contain the value 
     head=head.next; 
     size--; 
     result=true; 
    } 
    Node prev=head; 
    while ((prev.next != null)) {//actually checking prev.next if it contains the value 
     (prev.next.value == value){ 
      prev.next=prev.next.next; //remove link from prev to prev.next 
      size--; 
      result = true; 
     }else { 
      prev = prev.next; 
     } 
    } 
    return result; 
}