Java面试必备之ArrayList陷阱解析

public class TestListMain {

    public static void main(String[] args) {

        List<String> result = new ArrayList<>();
        result.add("a");
        result.add("b");
        result.add("c");
        result.add("d");

        for (String s : result) {
            if ("b".equals(s)) {
                result.remove("b");
            }
        }

    }
}

public class TestListMain {
    public TestListMain() {
    }

    public static void main(String[] args) {
        List<String> result = new ArrayList();
        result.add("a");
        result.add("b");
        result.add("c");
        result.add("d");
        //创建迭代器
        Iterator var2 = result.iterator();

        while(var2.hasNext()) {
            String s = (String)var2.next();
            if ("b".equals(s)) {
                result.remove("b");
            }
        }

    }
}

  public Iterator<E> iterator() {
        return new 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;

        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];
        }
     ...
     
 }

/**
 ***
 * For example, it is not generally permissible for one thread to modify a Collection
 * while another thread is iterating over it.  In general, the results of the
 * iteration are undefined under these circumstances.  Some Iterator
 * implementations (including those of all the general purpose collection implementations
 * provided by the JRE) may choose to throw this exception if this behavior is
 * detected.  Iterators that do this are known as <i>fail-fast</i> iterators,
 * as they fail quickly and cleanly, rather that risking arbitrary,
 * non-deterministic behavior at an undetermined time in the future.
 ***
**/
public class ConcurrentModificationException extends RuntimeException {
    ...
}

public class TestListMain {

    public static void main(String[] args) {

        List<String> result = new ArrayList<>();
        result.add("a");
        result.add("b");
        result.add("c");
        result.add("d");

       Iterator<String> iterator = list.iterator();
 
		while (iterator .hasNext()) {
			String str = iterator.next();
			if ("b".equals(str)) {
				iterator.remove();
			}
    }
}