How to split a string before calling another constructor

Question

I try to reuse my constructor like this:

    public final long x;
    public final long y;
    public final int level;
    private final int hash;
    public final Point tileCenter;

    public TileCoordinate(long x, long y, int level) {
        this.x = x;
        this.y = y;
        this.level = level;
        this.hash = Objects.hash(x, y, level);
        this.tileCenter = getTileCenter();
    }

    public TileCoordinate(String key) {
        String[] bits = key.split("-");
//      this.level = Integer.parseInt(bits[0]);
//      this.x = Long.parseLong(bits[1]);
//      this.y = Long.parseLong(bits[2]);
        this(Long.parseInt(bits[0]),Long.parseLong(bits[1]),Integer.parseLong(bits[2]));
        this.hash = Objects.hash(x, y, level);
        this.tileCenter = getTileCenter();
    }

Since I don't want to write this(Integer.parseInt(key.split("-")[0]),Long.parseLong(key.split("-")[1]),Long.parseLong(key.split("-")));, what are my options?

Would you mind clarifying what since i don't want to repeat key.split for every parameter means? You only have one parameter correct? — GBlodgett
– GBlodgett, Commented Jan 10, 2019 at 21:14
no, i mean i dont want to write this(Integer.parseInt(key.split("-")[0]),Long.parseLong(key.split("-")[1]),Long.parseLong(key.split("-"))); — wutzebaer
– wutzebaer, Commented Jan 10, 2019 at 21:14
Is that because the call to this must be the first statement in a constructor, if it exists? — rgettman
– rgettman, Commented Jan 10, 2019 at 21:16

rgettman · Accepted Answer · 2019-01-10 21:18:18Z

4

It looks like you're only doing this line String[] bits = key.split("-"); to avoid having to call it 3 times in the deferred constructor call to this(), which, if it exists, must be the first statement in a constructor.

Instead of delegating to a constructor for the actual field assignment, delegate to a private method that handles the field assignments.

public TileCoordinate(String key) {
    String[] bits = key.split("-");
    init(Long.parseInt(bits[0]),Long.parseLong(bits[1]),Integer.parseInt(bits[2]));
    this.hash = Objects.hash(x, y, level);
    this.tileCenter = getTileCenter();
}

private void init(long x, long y, int level) {
    // assign to fields here
}

Make sure it's private so it can't be overridden, where leaking this would become a problem.

You may also want to verify that bits has 3 elements before continuing.

answered Jan 10, 2019 at 21:18

rgettman

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2 Comments

wutzebaer Over a year ago

But the fields are final, forgot to tell this

rgettman Over a year ago

Well now that you've revealed that your fields are final, this won't work. In that case, a factory method would be the way to go.

Karol Dowbecki · Accepted Answer · 2019-01-10 21:18:26Z

3

The call to this() or super() must be the first statement in the constructor. One way to fix it would be to convert the second constructor into a Factory Method:

public static TileCoordinate parseTitleCoordinate(String key) {
  String[] bits = key.split("-");
  long x = Long.parseLong(bits[0]);
  long y = Long.parseLong(bits[1]);
  long level = Long.parseLong(bits[2]);
  return new TitleCoordinate(x, y, level);
}

This would allow to keep the fields final.

answered Jan 10, 2019 at 21:18

Karol Dowbecki

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1 Comment

nabster Over a year ago

Why super() is needed?

Zack · Accepted Answer · 2019-01-10 21:23:52Z

0

Could overload an init method:

  public TileCoordinate(long x, long y, int level) {
      init(x, y, level);
  }

  public TileCoordinate(String key) {
      init(key);
  }

  private void init(String key) { 
      String[] bits = key.split("-");
      init(Long.parseLong(bits[0]),
           Long.parseLong(bits[1]),
           Integer.parseInt(bits[2]));
  }

  private void init(long x, long y, int level) { 
      this.setX(x);
      this.setY(y);
      this.setLevel(level);
  }

This maintains single-responsibility. Only the 2nd init method is calling the setters, the rest are delegating.

answered Jan 10, 2019 at 21:23

Zack

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