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How do I check for equality of values?

I am starting with Java, so please refrain from doing this.

I have a class:

class Point {
  public int x;
  public int y;

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

I am creating two instances:

Point a = new Point(1, 1);
Point b = new Point(1, 1);

I want to check if these two points are in the same place. The obvious way,, if (a == b) { ... }

does not work as it sounds like "are the objects equal?" kind of test which is not what I want.

I can do if ( (a.x == b.x) && (a.y == b.y) ) { ... }

, but this solution is not very good.

How can I take two Point Objects and check for equality, coordinate in a wise, elegant way?

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2 answers


The standard protocol is to implement the method equals()

:

class Point {
  ...
  @Override
  public boolean equals(Object obj) {
    if (!(obj instanceof Point)) return false;
    Point rhs = (Point)obj;
    return x == rhs.x && y == rhs.y;
}

Then you can use a.equals(b)

.



Note that once you've done this, you also need to implement the method hashCode()

.

For classes like yours, I use Apache Commons Lang a lot EqualsBuilder

and HashCodeBuilder

:

class Point {
  ...

  @Override
  public boolean equals(Object obj) {
    return EqualsBuilder.reflectionEquals(this, obj);
  }

  @Override
  public int hashCode() {
    return HashCodeBuilder.reflectionHashCode(this);
  }
}
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You want to override the method hashCode()

and equals()

. If you are using Eclipse, you can make Eclipse do this by going to Source -> Generate hashCode() and equals()..

. After you override these methods, you can call:



if(a.equals(b)) { ... }
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