public class ArrayListDemo {    public static void main(String[] args) {//创建ArrayList集合对象        ArrayList<Student> array = new ArrayList<Student>();//创建学生对象        Student s1 = new Student("林青霞", 30);        Student s2 = new Student("张曼玉", 35);        Student s3 = new Student("王祖贤", 33);//把学生添加到集合        array.add(s1);        array.add(s2);        array.add(s3);//迭代器：集合特有的遍历方式        Iterator<Student> it = array.iterator();        while (it.hasNext()) {            Student s = it.next();            System.out.println(s.getName() + "," + s.getAge());        }        System.out.println("--------");//普通for：带有索引的遍历方式        for(int i=0; i<array.size(); i++) {            Student s = array.get(i);            System.out.println(s.getName() + "," + s.getAge());        }        System.out.println("--------");//增强for：最方便的遍历方式        for(Student s : array) {            System.out.println(s.getName() + "," + s.getAge());        }    }}

8.3 LinkedList集合的特有功能

9 java8中List根据某一字段去重

实体类：

package test;public class User {    private String userid;    private String username;    private String age;    private String address;        public User(String userid, String username, String age, String address) {        super();        this.userid = userid;        this.username = username;        this.age = age;        this.address = address;    }        public String getUserid() {        return userid;    }    public void setUserid(String userid) {        this.userid = userid;    }    public String getUsername() {        return username;    }    public void setUsername(String username) {        this.username = username;    }    public String getAge() {        return age;    }    public void setAge(String age) {        this.age = age;    }    public String getAddress() {        return address;    }    public void setAddress(String address) {        this.address = address;    }    @Override    public String toString() {        return "User [userid=" + userid + ", username=" + username + ", age=" + age + ", address=" + address + "]";    }}

测试：

package test;import java.util.ArrayList;import java.util.Comparator;import java.util.List;import java.util.TreeSet;import java.util.stream.Collectors;public class Test1 {    public static void main(String[] args) {        List<User> userList = new ArrayList<>();                userList.add(new User("1","李大锤","23","南京"));        userList.add(new User("2","张无忌","18","西安"));        userList.add(new User("3","刘德华","26","苏州"));        userList.add(new User("4","郭靖","33","上海"));                userList.add(new User("1","李大锤","23","南京"));    //id相同，其他数据也相同        userList.add(new User("3","带头大哥","36","杭州"));  //id相同，其他数据不同                System.out.println(userList);        //根据userid去重        userList = userList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(User :: getUserid))), ArrayList::new));        System.out.println(userList);    }}

测试结果：

[User [userid=1, username=李大锤, age=23, address=南京], User [userid=2, username=张无忌, age=18, address=西安], User [userid=3, username=刘德华, age=26, address=苏州], User [userid=4, username=郭靖, age=33, address=上海], User [userid=1, username=李大锤, age=23, address=南京], User [userid=3, username=带头大哥, age=36, address=杭州]][User [userid=1, username=李大锤, age=23, address=南京], User [userid=2, username=张无忌, age=18, address=西安], User [userid=3, username=刘德华, age=26, address=苏州], User [userid=4, username=郭靖, age=33, address=上海]]

可以看出，此操作把后面的两个id相同的都给剔除了。若两个id一样，其他数据不同的话，留下的数据是靠前的数据，剔除的是靠后的数据。

10 list简单去重

方案一:借助Set的特性进行去重

 	/**     * 去除重复数据     * 由于Set的无序性，不会保持原来顺序     * @param list     */    public static List<String> list distinct(List<String> list) {        final boolean sta = null != list && list.size() > 0;        List doubleList= new ArrayList();        if (sta) {            Set set = new HashSet();            set.addAll(list);            doubleList.addAll(set);        }        return doubleList;    }

方案二 : 利用set集合特性保持顺序一致去重

// Set去重并保持原先顺序的两种方法   public static void delRepeat(List<String> list) {   	   //方法一       List<String> listNew = new ArrayList<String>(new TreeSet<String>(list));       //方法二       List<String> listNew2 = new ArrayList<String>(new LinkedHashSet<String>(list));   }

方案三 : 使用list自身方法remove()–>不推荐

    /**     * 去除重复数据(一般不推荐)     * 类似于冒泡排序思想     * @param list     */  public static List<Map<String, Object>> distinct(List<Map<String, Object>> list) {        if (null != list && list.size() > 0) {        //循环list集合            for  ( int  i  =   0 ; i  <  list.size()  -   1 ; i ++ )  {                for  ( int  j  =  list.size()  -   1 ; j  >  i; j -- )  {                	// 这里是对象的比较，如果去重条件不一样，在这里修改即可                    if  (list.get(j).equals(list.get(i)))  {                        list.remove(j);                    }                }            }        }        //得到最新移除重复元素的list        return list;    }

方案四 : 遍历List集合,将元素添加到另一个List集合中

// 遍历后判断赋给另一个list集合，保持原来顺序public static List<String> delRepeat(List<String> list) {	  List<String> listNew = new ArrayList<String>();	  for (String str : list) {	       if (!listNew.contains(str)) {	           listNew.add(str);	       }	   }	  return listNew ;}

方案5 : 使用Java8特性去重

public static List<String> delRepeat(List<String> list) {     List<String> myList = list.stream().distinct().collect(Collectors.toList());	 return myList ;}