对象数组的重复项整理

首先定义一个实体类Person, 两个属性编号和姓名.

class Person {
    public Person(int id, String name) {
        this.id = id;
        this.name = name;
    }

    private int id;

    private String name;

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name == null ? null : name.trim();
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Person person = (Person) o;
        return id == person.id &&
                Objects.equals(name, person.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name);
    }

然后给person数组赋值，这里我故意写了几个重复数据。

 private static final List<Person> persons = new ArrayList<Person>() {{
        add(new Person(1, "zhangsan1"));
        add(new Person(2, "zhangsan2"));
        add(new Person(3, "zhangsan3"));
        add(new Person(4, "zhangsan4"));
        add(new Person(1, "zhangsan1"));
        add(new Person(4, "zhangsan4"));
        add(new Person(3, "zhangsan3"));
        add(new Person(4, "zhangsan4"));
    }};

最后在Main函数里对List数组进行去重处理

public static void main(String[] args) {
        Map<Person, List<Integer>> indexes = new HashMap<>();
        for (int i = 0; i < persons.size(); i++) {
            indexes.computeIfAbsent(persons.get(i), c -> new ArrayList<>()).add(i);
        }
        System.out.println(indexes);
    }

运行结果

{Person{id=4, name='zhangsan4'}=[3, 5, 7], Person{id=3, name='zhangsan3'}=[2, 6], Person{id=2, name='zhangsan2'}=[1], Person{id=1, name='zhangsan1'}=[0, 4]}