Shulou(Shulou.com)06/03 Report--

This article focuses on "how to remove elements from List". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how to remove elements from List.

I. exception code

Let's take a look at this code first. Have you ever written similar code?

Public static void main (String [] args) {

List list = new ArrayList ()

System.out.println ("start adding element size:" + list.size ())

For (int I = 0; I

< 100; i++) { list.add(i + 1); } System.out.println("元素添加结束 size:" + list.size()); Iterator iterator = list.iterator(); while (iterator.hasNext()) { Integer next = iterator.next(); if (next % 5 == 0) { list.remove(next); } } System.out.println("执行结束 size:" + list.size()); } 「毫无疑问，执行这段代码之后，必然报错，我们看下报错信息。」 我们可以通过错误信息可以看到，具体的错误是在checkForComodification 这个方法产生的。 二、ArrayList源码分析 首先我们看下ArrayList的iterator这个方法，通过源码可以发现，其实这个返回的是ArrayList内部类的一个实例对象。 public Iterator iterator() { return new Itr(); } 我们看下Itr类的全部实现。 private class Itr implements Iterator { int cursor; // index of next element to return int lastRet = -1; // index of last element returned; -1 if no such int expectedModCount = modCount; Itr() {} 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 ()

}

}

@ Override

@ SuppressWarnings ("unchecked")

Public void forEachRemaining (Consumer

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