java集合对字符串或对象去重

/**
* list去掉重复元素
*
* @param datas
* @return
*/
public static List<String> getNoDuplicate1(List<String> datas) {
List<String> res = new ArrayList<String>();
for (String single : datas) {
if (res.contains(single)) {
continue;
}
res.add(single);
}
return res;
}

/**
* 利用set进行去重
*
* @param datas
* @return
*/
public static List<String> getNoDuplicate2(List<String> datas) {
Set<String> targets = new HashSet<String>();
List<String> res = new ArrayList<String>();
for (String single : datas) {
if (targets.add(single)) {
res.add(single);
}
continue;
}
return res;
}

/**
* set和list转换去重
*
* @param datas
* @return
*/
public static List<String> getNoDuplicate3(List<String> datas) {
Set<String> sets = new HashSet<String>();
List<String> res = new ArrayList<String>();
sets.addAll(datas);
res.addAll(sets);
return res;
}

/**
* java8去重
*
* @param datas
* @return
*/
public static List<Object> getNoDuplicate4(List<String> datas) {
List<Object> res = datas.stream().distinct().collect(Collectors.toList());
return res;
}

/**
* 对象去重
* @param users
* @return
*/
public static ArrayList<User> removeDuplicateUser(List<User> users) {
Set<User> personSet = new TreeSet<User>(new Comparator<User>() {
public int compare(User o1, User o2) {
return o1.getUserName().compareTo(o2.getUserName());
}
});
personSet.addAll(users);
return new ArrayList<User>(personSet);
}

/**
* 双重for循环对对象去重
* @param users
* @return
*/
public static List<User> removeDuplicateRecr(List<User> users) {
List<User> res = users;
for (int i = 0; i < users.size()-1; i++) {
for (int j = users.size()-1; j > i; j--) {
if (users.get(j).getId() == users.get(i).getId()) {
users.remove(j);
}
}
}
return res;
}

/**
* 利用set不能重复的特性进行去重操作
* @param datas
* @return
*/
public static List<User> removeDupObjElementBySet(List<User> datas) {
Set<String> targets = new HashSet<String>();
List<User> res = new ArrayList<User>();
for (Usersingle : datas) {
if (targets.add(single.getId())) { //如果可以加进去，说明没有重复
targets.add(single.getId());
res.add(single);
}
continue;
}
return res;
}

/**
* 利用对象的hashCode码不相同进行去重
* @param datas
* @return
*/
public static List<User> removeDupObjElementByHash(List<User> datas) {
Set<Integer> targets = new HashSet<Integer>();
List<User> res = new ArrayList<User>();
for (Usersingle : datas) {
if (targets.add(single.hashCode())) { //如果可以加进去，说明没有重复
targets.add(single.hashCode());
res.add(single);
}
continue;
}
return res;
}

/**
* 对象去重,java8写法
* @param persons
* @return
*/
public static List<User> removeDupliByName(List<User> persons) {
Set<User> personSet = new TreeSet<User>((o1, o2) -> o1.getUserName().compareTo(o2.getUserName()));
personSet.addAll(persons);
return new ArrayList<User>(personSet);
}

/**
* 对象去重
* @param persons
* @return
*/
public static List<User> removeDupliByName2(List<User> persons) {
List<User> personList = new ArrayList<>();
persons.stream().forEach(p -> {
if (!personList.contains(p)) {
personList.add(p);
}
});
System.out.println(personList);
return personList;
}

/**
* 利用反射并通过获取属性和属性值的md5进行去重
* @param datas
* @return
*/
public static List<MdManageTree> removeDupElementByMd5(List<MdManageTree> datas){
Set<String> tems = new HashSet<>();
List<MdManageTree> resList = new ArrayList<>();
for(MdManageTree single : datas){
String elePropertyNameAndValue = reflectObject(single);
if(tems.add(strToMd5(elePropertyNameAndValue))){ //如果可以加进去，说明没有重复
tems.add(strToMd5(elePropertyNameAndValue));
resList.add(single);
}
continue;
}
return resList;
}

/**
* 获取字符串md5
* @param str
* @return
*/
public static String strToMd5(String str) {
MessageDigest md5 = null;
try {
md5 = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
logger.error("获取MD5对象失败");
}
try {
md5.update((str).getBytes("UTF-8"));
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
logger.error("MD5转换字节数组失败");
}
byte b[] = md5.digest();
int i;
StringBuffer buf = new StringBuffer("");
for(int offset=0; offset<b.length; offset++){
i = b[offset];
if(i<0){
i+=256;
}
if(i<16){
buf.append("0");
}
buf.append(Integer.toHexString(i));
}
return buf.toString();
}

/**
* java反射获取对象的属性值不为空的字符串拼接值
* @param obj
* @return
* @throws Exception
*/
public static String reflectObject(Object obj) {
Field[] field = obj.getClass().getDeclaredFields();
String result = "" ;
try{
for (int j = 0; j < field.length; j++) {
String name = field[j].getName();
name = name.substring(0, 1).toUpperCase() + name.substring(1);
Method m = obj.getClass().getMethod("get" + name);
String value = (String) m.invoke(obj);
if (value != null) {
result += name + value;
} else {
continue;
}
}
}catch (Exception e){
e.printStackTrace();
}
return result.trim();
}

public static void main(String[] args) {
List<String> nodes = new ArrayList<String>();
nodes.add("zhangsan");
nodes.add("lisi");
nodes.add("wangwu");
nodes.add("zhaoliu");
nodes.add("lisi");

List<User> res = new ArrayList<User>();
User user1 = new User();
user1.setUserId(1);
user1.setUserName("zhangsan");
user1.setPassWord("456");
res.add(user1);

User user2 = new User();
user2.setUserId(2);
user2.setUserName("lisi");
user2.setPassWord("345");
res.add(user2);

User user3 = new User();
user3.setUserId(3);
user3.setUserName("wangwu");
user3.setPassWord("778");
res.add(user3);

User user4 = new User();
user4.setUserId(1);
user4.setUserName("zhangsan");
user4.setPassWord("456");
res.add(user4);


//System.out.println(getNoDuplicate1(nodes));
//System.out.println(getNoDuplicate2(nodes));
//System.out.println(getNoDuplicate3(nodes));
//System.out.println(getNoDuplicate4(nodes));

//System.out.println(removeDuplicateUser(res));
System.out.println(removeDupliByName2(res));

}

user对象为:

private long userId;
private String userName;
private String passWord;


public long getUserId() {
return userId;
}
public void setUserId(long userId) {
this.userId = userId;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getPassWord() {
return passWord;
}
public void setPassWord(String passWord) {
this.passWord = passWord;
}

@Override
public boolean equals(Object o) {
if(this == o)return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
return Objects.equals(userName, user.getUserName()) && Objects.equals(passWord, user.getPassWord());


}
@Override
public String toString() {
return "User [userId=" + userId + ", userName=" + userName + ", passWord=" + passWord + "]";
}

实际使用中，equals方法可以根据自己需要重新定义；