Java: Search in ArrayList an element from object

Question

Let's say I have this:

    // Create arrayList
    ArrayList<Point> pointList = new ArrayList<Point>();

    // Adding some objects
    pointList.add(new Point(1, 1);
    pointList.add(new Point(1, 2);
    pointList.add(new Point(3, 4);

How can I get the index position of an object by searching one of its parameters? ~~I tried this but doesn't work.~~

~~pointList.indexOf(this.x(1));~~

Thanks in advance.

Didn't know how to explain. Forget it. =)

Javier Provecho Fernández
– Javier Provecho Fernández

2012-12-31 20:08:10 +00:00
Commented Dec 31, 2012 at 20:08 — Javier Provecho Fernández
– Javier Provecho Fernández, Commented Dec 31, 2012 at 20:08

arshajii · Accepted Answer · 2012-12-31 19:54:05Z

3

You have to loop through the list yourself:

int index = -1;

for (int i = 0; i < pointList.size(); i++)
    if (pointList.get(i).x == 1) {
        index = i;
        break;
    }

// now index is the location of the first element with x-val 1
// or -1 if no such element exists

answered Dec 31, 2012 at 19:54

arshajii

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1 Comment

Javier Provecho Fernández Over a year ago

Thanks for your answer, it worked as expected. Why I didn't think that before? Your answer was first of all. Marked as correct.

user1131435 · Accepted Answer · 2012-12-31 19:54:47Z

1

You need to create a custom loop to do that.

public int getPointIndex(int xVal) {
    for(int i = 0; i < pointList.size(); i++) {
        if(pointList.get(i).x == xVal) return i;
    }
    return -1; //Or throw error if it wasn't found.
}

answered Dec 31, 2012 at 19:54

user1131435

4 Comments

BeeOnRope Over a year ago

null is not a valid return type for int.

user1131435 Over a year ago

Whoops, fixed. There's two hours of sleep for you.

Javier Provecho Fernández Over a year ago

Thanks for your answer. Same as A. R. S. but in a method. It worked.

user1131435 Over a year ago

No problem! Didn't mean to post a duplicate, but got ninja'd :P

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