看吧！ HashMap 一边循环一边删除，这不就出问题了！
程序员内点事
共 14710字，需浏览 30分钟
·
2024-07-30 08:39
foreach循环？
public class HashMapIteratorDemo {
String[] arr = {"aa", "bb", "cc"};
public void test1() {
for(String str : arr) {
}
}
}
public class HashMapIteratorDemo2 {
String[] arr = {"aa", "bb", "cc"};
public void test1() {
for(int i = 0; i < arr.length; i++) {
String str = arr[i];
}
}
}
public class HashMapIteratorDemo3 {
List<Integer> list = new ArrayList<>();
public void test1() {
list.add(1);
list.add(2);
list.add(3);
for(Integer var : list) {
}
}
}
public class HashMapIteratorDemo4 {
List<Integer> list = new ArrayList<>();
public void test1() {
list.add(1);
list.add(2);
list.add(3);
Iterator<Integer> it = list.iterator();
while(it.hasNext()) {
Integer var = it.next();
}
}
}
HashMap遍历集合并对集合元素进行remove、put、add
1、现象
public class HashMapIteratorDemo5 {
public static void main(String[] args) {
Map<Integer, String> map = new HashMap<>();
map.put(1, "aa");
map.put(2, "bb");
map.put(3, "cc");
for(Map.Entry<Integer, String> entry : map.entrySet()){
int k=entry.getKey();
String v=entry.getValue();
System.out.println(k+" = "+v);
}
}
}
public class HashMapIteratorDemo5 {
public static void main(String[] args) {
Map<Integer, String> map = new HashMap<>();
map.put(1, "aa");
map.put(2, "bb");
map.put(3, "cc");
for(Map.Entry<Integer, String> entry : map.entrySet()){
int k=entry.getKey();
if(k == 1) {
map.put(1, "AA");
}
String v=entry.getValue();
System.out.println(k+" = "+v);
}
}
}
public class HashMapIteratorDemo5 {
public static void main(String[] args) {
Map<Integer, String> map = new HashMap<>();
map.put(1, "aa");
map.put(2, "bb");
map.put(3, "cc");
for(Map.Entry<Integer, String> entry : map.entrySet()){
int k=entry.getKey();
if(k == 1) {
map.put(4, "AA");
}
String v=entry.getValue();
System.out.println(k+" = "+v);
}
}
}
2、细究底层原理
final Node<K,V> nextNode() {
Node<K,V>[] t;
Node<K,V> e = next;
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
if (e == null)
throw new NoSuchElementException();
if ((next = (current = e).next) == null && (t = table) != null) {
do {} while (index < t.length && (next = t[index++]) == null);
}
return e;
}
public V remove(Object key) {
Node<K,V> e;
return (e = removeNode(hash(key), key, null, false, true)) == null ?
null : e.value;
}
public final boolean remove(Object key) {
return removeNode(hash(key), key, null, false, true) != null;
}
public final boolean remove(Object o) {
if (o instanceof Map.Entry) {
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
Object key = e.getKey();
Object value = e.getValue();
return removeNode(hash(key), key, value, true, true) != null;
}
return false;
}
public final void remove() {
Node<K,V> p = current;
if (p == null)
throw new IllegalStateException();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
current = null;
K key = p.key;
removeNode(hash(key), key, null, false, false);
expectedModCount = modCount; //----------------这里将expectedModCount 与modCount进行同步
}
final Node<K,V> removeNode(int hash, Object key, Object value,
boolean matchValue, boolean movable) {
Node<K,V>[] tab; Node<K,V> p; int n, index;
if ((tab = table) != null && (n = tab.length) > 0 &&
...
if (node != null && (!matchValue || (v = node.value) == value ||
(value != null && value.equals(v)))) {
if (node instanceof TreeNode)
((TreeNode<K,V>)node).removeTreeNode(this, tab, movable);
else if (node == p)
tab[index] = node.next;
else
p.next = node.next;
++modCount; //------------------------这里对modCount进行了自增，可能会导致后面与expectedModCount不一致
--size;
afterNodeRemoval(node);
return node;
}
}
return null;
}
public class HashMapIteratorDemo5 {
public static void main(String[] args) {
Map<Integer, String> map = new HashMap<>();
map.put(1, "aa");
map.put(2, "bb");
map.put(3, "cc");
// for(Map.Entry<Integer, String> entry : map.entrySet()){ // int k=entry.getKey(); // // if(k == 1) {// map.put(1, "AA");// }// String v=entry.getValue(); // System.out.println(k+" = "+v); // }
Iterator<Map.Entry<Integer, String>> it = map.entrySet().iterator();
while(it.hasNext()){
Map.Entry<Integer, String> entry = it.next();
int key=entry.getKey();
if(key == 1){
it.remove();
}
}
}
}
作者：你呀不牛
链接：https://juejin.cn/post/7114669787870920734 我是小富～ 下期见！
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