java - 如何在 android 中获取 indexof(object) 请参阅我的示例以了解

Question

请阅读此示例以了解我的问题，谢谢。

像这样向arraylist添加一些数据后：

ArrayList<UserInfo> user_info = new ArrayList<>();
user_info.add(new UserInfo(1, "alex", "26"));
user_info.add(new UserInfo(2, "daniel", "23"));
user_info.add(new UserInfo(3, "veka", "19"));

我想获得“veka”的索引，我该怎么做？我知道如何使用 get index of 来处理数组字符串，但我如何使用带有UserInfo的示例来做到这一点

谢谢。

这是UserInfo.class

public class UserInfo {

private int id;
private String UserName;
private String UserAge;

public UserInfo(int id, String userName, String userAge) {
    this.id = id;
    UserName = userName;
    UserAge = userAge;
}

public int getId() {
    return id;
}

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

public String getUserName() {
    return UserName;
}

public void setUserName(String userName) {
    UserName = userName;
}

public String getUserAge() {
    return UserAge;
}

public void setUserAge(String userAge) {
    UserAge = userAge;
}
}

标签： javaandroidandroid-studio

Answer 1

You should implement the override the equals method. This will be used by the indexOf function.

An example is here

public class Point {

    int x; 
    int y;

    public Point(int a, int b) {
    this.x=a;this.y=b;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + x;
        result = prime * result + y;
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Point other = (Point) obj;
        if (x != other.x)
            return false;
        if (y != other.y)
            return false;
        return true;
    }       
}

ArrayList<Point> p=new ArrayList<Point>();

Point p1 = new Point(3,4);
Point p2 = new Point(1,2);

p.add(new Point(3,4));
p.add(new Point(1,2));

System.out.println(p.indexOf(p1));

With this information you can update your class and then it will work.