关于JAVA Iterator的一点理解

最新推荐文章于 2025-05-29 14:53:26 发布

原创最新推荐文章于 2025-05-29 14:53:26 发布 · 314 阅读

1 ·

CC 4.0 BY-SA版权

JAVA 专栏收录该内容

93 篇文章

订阅专栏

本文详细解析了如何使用Iterator遍历JSONArray和JSONObject，通过实现ListIterator接口，利用JSONArrayListIterator类，展示了遍历过程中的核心代码片段。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

Iterator是一个接口，里边有4个方法：

hasNext();next();remove();forEachRemaining();

我们一般可以用Iterator来遍历JSONArray，那是因为，JSONArray类实现了List接口，而List接口继承了Iterable

而Iterbale接口中，有Iterator<T> iterator()方法，List也拥有Iterator<T> iterator()方法，所以JSONArray必须实现Iterator<T> iterator()方法，如图：

    public Iterator iterator() {
        return new JSONArray.JSONArrayListIterator();
    }

JSONArray的Iterator<T> iterator()方法是借助JSONArrayListIterator类实现的。（JSONArrayListIterator类实现了ListIterator接口，而ListIterator接口正是继承了Iterbale接口，因此ListIterator也拥有Iterator<T> iterator()抽象方法，作为ListIterator的实现类，JSONArrayListIterator必须实现Iterator<T> iterator()抽象方法）

来看看它具体是怎样实现的：

private class JSONArrayListIterator implements ListIterator {
        int currentIndex = 0;
        int lastIndex = -1;

        JSONArrayListIterator() {
        }

        JSONArrayListIterator(int index) {
            this.currentIndex = index;
        }

        public boolean hasNext() {
            return this.currentIndex != JSONArray.this.size();
        }

        public Object next() {
            try {
                Object next = JSONArray.this.get(this.currentIndex);
                this.lastIndex = this.currentIndex++;
                return next;
            } catch (IndexOutOfBoundsException var2) {
                throw new NoSuchElementException();
            }
        }

        public void remove() {
            if (this.lastIndex == -1) {
                throw new IllegalStateException();
            } else {
                try {
                    JSONArray.this.remove(this.lastIndex);
                    if (this.lastIndex < this.currentIndex) {
                        --this.currentIndex;
                    }

                    this.lastIndex = -1;
                } catch (IndexOutOfBoundsException var2) {
                    throw new ConcurrentModificationException();
                }
            }
        }

        public boolean hasPrevious() {
            return this.currentIndex != 0;
        }

        public Object previous() {
            try {
                int index = this.currentIndex - 1;
                Object previous = JSONArray.this.get(index);
                this.lastIndex = this.currentIndex = index;
                return previous;
            } catch (IndexOutOfBoundsException var3) {
                throw new NoSuchElementException();
            }
        }

        public int nextIndex() {
            return this.currentIndex;
        }

        public int previousIndex() {
            return this.currentIndex - 1;
        }

        public void set(Object obj) {
            if (this.lastIndex == -1) {
                throw new IllegalStateException();
            } else {
                try {
                    JSONArray.this.set(this.lastIndex, obj);
                } catch (IndexOutOfBoundsException var3) {
                    throw new ConcurrentModificationException();
                }
            }
        }

        public void add(Object obj) {
            try {
                JSONArray.this.add(this.currentIndex++, obj);
                this.lastIndex = -1;
            } catch (IndexOutOfBoundsException var3) {
                throw new ConcurrentModificationException();
            }
        }
    }

了然了。。。

因此，我们可以用下面的代码遍历JSONArray

        Person person = new Person("wang","18","man");
        Person person1 = new Person("li","17","man");
        List<Person> people = new ArrayList<>();
        people.add(person);
        people.add(person1);       
        JSONArray jsonArray = JSONArray.fromObject(people);
        Iterator iterator2 = jsonArray.iterator();
        while (iterator2.hasNext())
        {
//            System.out.println(iterator2.next().toString());
            System.out.println(((JSONObject)iterator2.next()).get("age").toString());
        }

用下面的代码遍历JSONObject

        //遍历JSONObject
        JSON json = net.sf.json.JSONObject.fromObject(person);
        Iterator iterator = ((JSONObject) json).keys();
        while (iterator.hasNext())
        {
            String key = iterator.next().toString();
            Object obj = ((JSONObject) json).get(key);
        }