Java uses LRUMap to remove duplicate values in List

I am currently working on a traceability project to summarize some of the things encountered.

List<entityInfo> entities = new ArrayList<entityInfo>();//需去除list中实体的num属性的重复值
private Map<String, String> map = Collections.synchronizedMap(new LRUMap(100));//取100个键值对，采用LRU（最近最少使用）原则。由于LRUMap线程不安全，外面封装一个Collections.synchronizedMap()可保证线程安全。
int size = entities.size();
for (int i = 0; i < size; i++) {
//判断map中是否存在相同key，若存在，则为重复值。
if(map.containsKey(entities.get(i).getNum()) {
			    System.out.println("不重复值")
			}else {
			 	System.out.println("重复值")
			    map.put(entities.get(i).getNum(), entities.get(i).getNum());
			}
}