Databases
StackOverflow2013
Postsdbo
POConstructor that can either make a copy or reference
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POConstructor that can either make a copy or reference
    primarykey
    data
    text
    <p>The code below shows a rectangle class using <code>double</code> points, which are also stored in an object. The rectangle and the points in the rectangle are immutable because they do not need to change. I would like to provide the ability to copy (make new point objects) or make a reference to the points provided in the constructor, but the only way I could think of doing this is to add a boolean parameter specifying if the caller wants to make a copy or reference. </p> <p>This is for extensibility, although it may not be of prime importance, I would like this option. However, I don't like the way it's implemented with the boolean parameter. Is there a way I can make two constructors taking the same parameters, one to make a reference and one to make copies? or is there an equivalent to C++ parameter auto definition in the prototype so it doesn't need to be specified by the caller? I have thought about using varargs, but then the caller could send unlimited parameters as garbage, possibly causing a stack overflow, I think...</p> <pre><code>/** * An immutable, double-precision floating-point (64-bit doubles x4) rectangle. * The rectangle can be made to reference existing points, or to create new points. Since the points * are also immutable, this is acceptable, as it is guaranteed they cannot change. * @author Bill */ public class DoubleRect { public final DoublePoint topLeft; public final DoublePoint bottomRight; public DoubleRect(DoublePoint setTopLeft, DoublePoint setBottomRight, boolean makeCopies) { if(makeCopies == true) { topLeft = new DoublePoint(setTopLeft); bottomRight = new DoublePoint(setBottomRight); } else { topLeft = setTopLeft; bottomRight = setBottomRight; } } } </code></pre> <p><strong>UPDATE: Thanks to all that helped me figure out what to do instead. This is how I recoded it.</strong></p> <pre><code>/** * An immutable, double-precision floating-point (64-bit) rectangle. * The rectangle can be made to reference existing points, or to create new points. Since the points * are also immutable, referencing the points is acceptable, as it is guaranteed they cannot change. * @author Bill */ public class DoubleRect { public final DoublePoint topLeft; public final DoublePoint bottomRight; /** * This constructor will reference the passed objects rather than duplicating them. * See the static factory method createWithClonedPoints() for making internal copies of the point objects * @param setTopLeft Double point designating the top left coordinate * @param setBottomRight Double point designating the bottom right coordinate */ public DoubleRect(DoublePoint setTopLeft, DoublePoint setBottomRight) { topLeft = setTopLeft; bottomRight = setBottomRight; } /** * This constructor will create new immutable points within this object using the coordinates specified */ public DoubleRect(double top, double left, double right, double bottom) { topLeft = new DoublePoint(left, top); bottomRight = new DoublePoint(right, bottom); } public static DoubleRect createWithClonedPoints(DoublePoint topLeft, DoublePoint bottomRight) { return new DoubleRect(topLeft.x, topLeft.y, bottomRight.x, bottomRight.y); } } </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USWilliam the Coderer
    1. USWilliam the Coderer
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POConstructor that can either make a copy or reference
      1. This table or related slice is empty.
      1. VTUpMod
    1. COIf they are immutable then why make copies?
      singulars
      1. POConstructor that can either make a copy or reference
      1. USBhesh Gurung
    2. COnot sure yet... it is for use in a multi-thread app, and possibly may want to use it in multi-process later. I'm fairly new to Java, and I'm used to pointers.
      singulars
      1. POConstructor that can either make a copy or reference
      1. USWilliam the Coderer
    3. COUse a static factory method.
      singulars
      1. POConstructor that can either make a copy or reference
      1. USDave Newton
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload