使用迭代器删除的坑

如图方式遍历删除集合元素,会抛出 java.lang.IllegalStateException

			package jihe;
			
			import typeinfo.pets.Mutt;
			import typeinfo.pets.Pet;
			import typeinfo.pets.Pets;
			import typeinfo.pets.Rat;
			
			import java.util.ArrayList;
			import java.util.Arrays;
			import java.util.Iterator;
			import java.util.List;
			
			public class SimpleIteration {
			    public static void main(String[] args) {
			
			        /*while (it.hasNext()) {
			            Pet p = it.next();
			            System.out.println(p.id() + ":" + p + " ");
			        }
			        System.out.println();
			        for (Pet p : pets) {
			
			            System.out.println(p.id() + ":" + p + " ");
			        }
			
			        System.out.println();
			        it = pets.iterator();*/
			
			       /* for (int i = 0; i < 12; i++) {
			
			            it.next();
			            it.remove();
			        }*/
			        List<Pet> pets = Pets.arrayList(12);
			
			        System.out.println(pets);// [Rat, Manx, Cymric, Mutt, Pug, Cymric, Pug, Manx, Cymric, Rat, EgyptianMau, Hamster]
			        Iterator<Pet> it = pets.iterator();
			       while (it.hasNext()){
			          // it.next();
			            it.remove();
			        }
			        //  java.lang.IllegalStateException 备注：先使用it.hasNext()  在使用it.next()
			
			        System.out.println(pets);// [Pug, Manx, Cymric, Rat, EgyptianMau, Hamster]
			    }
			}

去看源码,就是line:863-864

lastRet 就是上次上次操作的最后角标,默认初始化时-1;

hasNext()方法不会改变 lastRet 字段的值;所以在执行remove()方法时会抛出异常;

next()方法,返回当前的元素,并将lastRet 的值改变为当前光标值cursor(一般刚开始是0);