Java List实体类去重

今天写了一段代码判断list中是否包含某个实体openSubjectDTO,不包含就添加进去,发现不好使

if(!subjectList.contains(openSubjectDTO)){
subjectList.add(openSubjectDTO);
}

后来发现是openSubjectDTO类中缺少两个方法如下:

List 去除重复Object对象：

    对象重复是指对象里面的变量的值都相等，并不定是地址。list集合存储的类型是基础类型还比较好办，直接把list集合转换成set集合就会自动去除。

   当set集合存储的是对象类型时，需要在对象的实体类里面重写public boolean equals(Object obj) {} 和 public int hashCode() {} 两个方法。

List特点：元素有放入顺序，元素可重复 

Map特点：元素按键值对存储，无放入顺序 

Set特点：元素无放入顺序，元素不可重复（注意：元素虽然无放入顺序，但是元素在set中的位置是有该元素的HashCode决定的，其位置其实是固定的） 

新建一个实体类

public class User {
    private String id;
    private String name;
    private String age;
    private String address;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    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 int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        result = prime * result + ((age == null) ? 0 : age.hashCode());
        result = prime * result + ((address == null) ? 0 : address.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        User other = (User) obj;
        if (id == null) {
            if (other.id != null) {
                return false;
            }
        } else if (!id.equals(other.id)) {
            return false;
        }
        if (name == null) {
            if (other.name != null) {
                return false;
            }
        } else if (!name.equals(other.name)) {
            return false;
        }
        if (age == null) {
            if (other.age != null) {
                return false;
            }
        } else if (!age.equals(other.age)) {
            return false;
        }
        if (address == null) {
            if (other.address != null) {
                return false;
            }
        } else if (!address.equals(other.address)) {
            return false;
        }
        return true;
    }
}

调用即可

private static List<User> removeListDuplicateObject(List<User> list) {
    System.out.println(Arrays.toString(list.toArray()));
    Set<User> set = new HashSet<User>();
    set.addAll(list);
    System.out.println(Arrays.toString(set.toArray()));
    List<User> listnewList = new ArrayList<User>(set);
    return listnewList;
    }