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删除集合中的元素
public class testzhu {
public static void main(String[] args) {
List<Integer> integerList = new ArrayList<>(Arrays.asList(1,2,3,4,5,6,7,8));
for(int i = 0 ; i < integerList.size() ; i++){
integerList.remove(i); // 本意是将集合中的元素全部删除
// 代码运行过程中,集合本身在不断变更,下标同时也在变更
}
System.out.println(integerList);
// [2, 4, 6, 8]
}
}
参考资料
注意事项
// 删除全部元素
// 此时提示异常
public class testzhu {
public static void main(String[] args) {
List<Integer> integerList = new ArrayList<>(Arrays.asList(1,2,3,4,5,6,7,8));
Iterator<Integer> iterator = integerList.iterator();
while (iterator.hasNext()){
iterator.remove();
// Exception in thread "main" java.lang.IllegalStateException
// at java.util.ArrayList$Itr.remove(ArrayList.java:844)
// at test.testzhu.main(testzhu.java:23)
}
System.out.println(integerList);
}
}
- 异常分析
/**
* An optimized version of AbstractList.Itr
*/
private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;
public boolean hasNext() {
return cursor != size;
}
@SuppressWarnings("unchecked")
public E next() {
checkForComodification();
int i = cursor;
if (i >= size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[lastRet = i];
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
- 直接调用 Itr 中的 remove 方法,此时 lastRet 初始化值为 -1 会抛出异常
- 需要调用 Itr 中的 next 方法
- cursor 为当前游标指向
- 方法内将集合中的元素进行拷贝赋值给了 elementData ,保证原有集合中数据不变
- lastRet = i 进行出行赋值
- 调用 next 后再调用 remove 方法
public class testzhu {
public static void main(String[] args) {
List<Integer> integerList = new ArrayList<>(Arrays.asList(1,2,3,4,5,6,7,8));
Iterator<Integer> iterator = integerList.iterator();
while (iterator.hasNext()){
Integer next = iterator.next();
if(next % 1 == 0){
iterator.remove();
}
}
System.out.println(integerList);
}
}