Map相关

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循环输出HashMap内容

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private static void loogerHashMapContent() {
    HashMap<String, Object> hashMap = new HashMap<String, Object>();
    hashMap.put("carrier", "carrier1");
    hashMap.put("province", "province1");
    hashMap.put("ismodem", "ismodem1");
    hashMap.put("state", "state1");


    Iterator<Entry<String, Object>> iterator = hashMap.entrySet().iterator();
    while (iterator.hasNext()) {
        Entry<String, Object> entry = iterator.next();
        System.out.print(entry.getKey()+":"+entry.getValue()+",");
    }
    System.out.println();
}

HashMap遍历

原文地址

第一种:

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Map map = new HashMap();
Iterator iter = map.entrySet().iterator();
while (iter.hasNext()) {
    Map.Entry entry = (Map.Entry) iter.next();
    Object key = entry.getKey();
    Object val = entry.getValue();
}

效率高,以后一定要使用此种方式！
第二种:

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Map map = new HashMap();
Iterator iter = map.keySet().iterator();
while (iter.hasNext()) {
    Object key = iter.next();
    Object val = map.get(key);
}

效率低,以后尽量少使用！

HashMap遍历

第一种：for each map.entrySet()

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Map<String, String> map = new HashMap<String, String>();
for (Entry<String, String> entry : map.entrySet()) {
    entry.getKey();
    entry.getValue();
}

第二种：显式调用map.entrySet()的集合迭代器

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Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();
while(iterator.hasNext()){
    Map.Entry<String, String> entry = iterator.next();
    entry.getKey();
    entry.getValue();
}

第三种：for each map.keySet()，再调用get获取

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Map<String, String> map = new HashMap<String, String>();
for(String key: map.keySet()){
    map.get(key);
}

第四种：for each map.entrySet()，用临时变量保存map.entrySet()

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Set<Entry<String, String>> entrySet = map.entrySet();
for (Entry<String, String> entry : entrySet) {
    entry.getKey();
    entry.getValue();
}

经过1万、10万、100万、200万的循环遍历，比较它们的耗时，得出结论：

  1. 既需要key也需要value，直接用
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Map<String, String> map = new HashMap<String, String>();
for (Map.Entry<String, String> entry : map.entrySet()) {
    entry.getKey();
    entry.getValue();
}
  1. 如果只是遍历key而无需value的话，可以直接用
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Map<String, String> map = new HashMap<String, String>();
for (String key : map.keySet()) {
	// key process
}

Map转url参数

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private String convertToUrlParams(Map<String, Object> map) {
    if (map == null || map.size() <= 0) {
        return "";
    }
    StringBuilder stringBuilder = new StringBuilder();
    for (Map.Entry<String, Object> entry : map.entrySet()) {
        if (!TextUtils.isEmpty(stringBuilder)) {
            stringBuilder.append("&");
        }
        stringBuilder.append(entry.getKey()).append("=").append(entry.getValue());
    }
    return stringBuilder.toString();
}