1.List集合中的数据类型是基本数据类型

可以直接将list集合转换成set，就会自动去除重复的元素。

如下示例：

public class Test {
    public static void main(String[] args) {
        List list = new ArrayList();
        list.add(11);
        list.add(12);
        list.add(13);
        list.add(14);
        list.add(15);
        list.add(11);
        System.out.println(list);
        Set set = new HashSet();
        List newList = new ArrayList();
        set.addAll(list);
        newList.addAll(set);
        System.out.println(newList);
    }
}

2.List集合中存储的数据类型是对象类型

需要在对象的实体类中去重写equals()方法和hashCode()方法

public class People {
    private String name;
    private String phoneNumber;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPhoneNumber() {
        return phoneNumber;
    }
    public void setPhoneNumber(String phoneNumber) {
        this.phoneNumber = phoneNumber;
    }
    public People(String name, String phoneNumber) {
        super();
        this.name = name;
        this.phoneNumber = phoneNumber;
}
    @Override
    public String toString() {
        return "People{" +
                "name='" + name + ''' +
                ", phoneNumber='" + phoneNumber + ''' +
                '}';
    }
    @Override
    public boolean equals(Object o) {
        People p = (People) o;
        return name.equals(p.name) && phoneNumber.equals(p.phoneNumber);
    }
    @Override
    public int hashCode() {
        String str = name + phoneNumber;
        return str.hashCode();
    }
}
public static void main(String[] args) {
    List<People> listPeople = new ArrayList<People>();
    listPeople.add(new People("张三", "11111"));
    listPeople.add(new People("张三",  "22222"));
    listPeople.add(new People("李四",  "33333"));
    listPeople.add(new People("张三",  "22222"));
    Set<People> setData = new HashSet<People>();
    setData.addAll(listPeople);
    System.out.println("list：" + listPeople.toString());
    System.out.println("set：" + setData.toString());
}

最后，我们拿出String中的equals()方法和hashCode()方法源码来加深认识：

equals()

    public boolean equals(Object anObject) {
        if (this == anObject) {
            return true;
        }
        if (anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = count;
            if (n == anotherString.count) {
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = offset;
                int j = anotherString.offset;
                while (n-- != 0) {
                    if (v1[i++] != v2[j++])
                        return false;
                }
                return true;
            }
        }
        return false;
    }

比较两个对象时，首先先去判断两个对象是否具有相同的地址，如果是同一个对象的引用，则直接放回true；如果地址不一样，则证明不是引用同一个对象，接下来就是挨个去比较两个字符串对象的内容是否一致，完全相等返回true，否则false。

hashCode()

    public int hashCode() {
        int h = hash;
        if (h == 0 && count > 0) {
            int off = offset;
            char val[] = value;
            int len = count;
            for (int i = 0; i < len; i++) {
                h = 31*h + val[off++];
            }
            hash = h;
        }
        return h;
    }