Java Map的幾種遍歷方法
阿新 • • 發佈:2018-11-08
Map key重複則會出現最後一次put的value //HashMap TreeMap
Map<Object, Object> map = new HashMap<Object, Object>();
Iterator<Map.Entry<Object, Object>> it = map.entrySet().iterator();
while(it.hasNext()){
Entry<Object, Object> entry = it.next();
System.out.println("key:"+entry.getKey()+":"+"value"+entry.getValue());
}
for(Object key:map.keySet()){
System.out.println("key:"+key+":"+"value"+map.get(key));
}
System.out.println("key:"+entry.getKey()+":"+"value"+entry.getValue());
}
Set<Object> keySet = map.keySet();
如果只需要遍歷key或value,那採用4方法速度是最快的
除去該種情況,推薦使用3方法,速率相對來說最好
1方法肯定能用
2方法據鍵取value遍歷速率不理想
遍歷Map
Map<Object, Object> map = new HashMap<Object, Object>();
1.老版本遍歷,泛型1.5以上 ,可以進行entry移除的操作
//iterator.remove();Iterator<Map.Entry<Object, Object>> it = map.entrySet().iterator();
while(it.hasNext()){
Entry<Object, Object> entry = it.next();
System.out.println("key:"+entry.getKey()+":"+"value"+entry.getValue());
}
2. 1.5以上
System.out.println("key:"+key+":"+"value"+map.get(key));
}
3.
for(Map.Entry<Object, Object> entry:map.entrySet()){System.out.println("key:"+entry.getKey()+":"+"value"+entry.getValue());
}
4.只進行key或value遍歷,視具體情況
Collection<Object> values = map.values();Set<Object> keySet = map.keySet();
總結:
除去該種情況,推薦使用3方法,速率相對來說最好
1方法肯定能用
2方法據鍵取value遍歷速率不理想