迴圈刪除集合中合格元素_迴圈刪除集合中合格元素

最初以為用一個簡單的for迴圈就解決了，但忽略了移除後會改變集合的大小發生一些越界的錯誤或者資料不對；

正確的方式：迭代器Iterator；下面是網上的一個小例子；最後貼出自己錯誤的代碼協助記憶。

import java.util.ArrayList;import java.util.Iterator;public class TestList {public static void main(String[] args) {test1();test2();test3();}public static void test1() {ArrayList<String> list = new ArrayList<String>();list.add("one");list.add("two");list.add("two");list.add("two");list.add("two");for (int i = 0; i < list.size(); i++) {if (list.get(i).equals("two")) {list.remove(i);}}System.out.println("test1 : " + list);}public static void test2() {ArrayList<String> list = new ArrayList<String>();list.add("one");list.add("two");list.add("two");list.add("two");list.add("two");for (String s : list) {if (s.equals("two")) {list.remove(s);}}System.out.println("test2 : " + list);}public static void test3() {ArrayList<String> list = new ArrayList<String>();list.add("one");list.add("two");list.add("two");list.add("two");list.add("two");Iterator<String> iter = list.iterator();while (iter.hasNext()) {String s = iter.next();if (s.equals("two")) {iter.remove();}}System.out.println("test3 : " + list);}}

第一個方法輸出

test1 : [one, two, two]

第二個方法報錯

Exception in thread "main" Java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
at java.util.AbstractList$Itr.next(AbstractList.java:343)
at TestList.test2(TestList.java:34)
at TestList.main(TestList.java:8)

第三個方法輸出

test3 : [one]

第三種的結果是正確的；

註：自己錯誤例子

//查詢商戶下面所有板塊規則if(wmPlates != null && wmPlates.size() > 0) { //for迴圈的這個是錯誤的；同時對集合的判空做很差；會出現錯誤資料或者直接拋出異常for (int i = 0; i < wmPlates.size(); i++) {WmTablebookruleExample example = new WmTablebookruleExample();example.createCriteria().andStoreIdEqualTo(Integer.parseInt(storeId)).andPlateIdEqualTo(wmPlates.get(i).getId()).andStatusEqualTo(0).andIsDeleteEqualTo(0);List<WmTablebookrule> tableRuleList = tablebookruleService.selectByExample(example);if(tableRuleList != null && tableRuleList.size() > 0) {        } else {wmPlates.remove(i);}}Iterator<WmPlate> it = wmPlates.iterator();  while(it.hasNext()){  WmPlate plate = it.next();  WmTablebookruleExample example = new WmTablebookruleExample();example.createCriteria().andStoreIdEqualTo(Integer.parseInt(storeId)).andPlateIdEqualTo(plate.getId()).andStatusEqualTo(0).andIsDeleteEqualTo(0); List<WmTablebookrule> tableRuleList = tablebookruleService.selectByExample(example); if(null == tableRuleList || tableRuleList.size() == 0) { it.remove();} } }