JSONObject 几个方法的区别

public Object put(Object key,Object value) 将value映射到key下。如果此JSONObject对象之前存在一个value在这个key下，当前的value会替换掉之前的value
Associates the specified value with the specified key in this map(optional operation). If the map prevIoUsly contained . a mapping for this key,the old value is replaced by the specified value. (A mapmis said to contain a mapping for a key kif and only if m.containsKey(k) would returntrue.))

public JSONObject accumulate(String key,Object value) 累积value到这个key下。这个方法同element()方法类似，特殊的是，如果当前已经存在一个value在这个key下那么一个JSONArray将会存储在这个key下来保存所有累积的value。如果已经存在一个JSONArray，那么当前的value就会添加到这个JSONArray中
。相比之下replace方法会替代先前的value
Accumulate values under a key. It is similar to the element method except that if there is already an object stored
under the key then a JSONArray is stored under the key to hold all of the accumulated values. If there is already a
JSONArray,then the new value is appended to it. In contrast,the replace method replaces the prevIoUs value.

public JSONObject element(String key,Object value) 将键/值对放到这个JSONObject对象里面。如果当前value为空(null)，那么如果这个key存在的话，这个key就会移除掉。