JEP Draft: Enhanced Local Variable Declarations

(openjdk.org)

2 points | by mfiguiere 7 hours ago ago

2 comments

$Someone 6 hours ago
FTA:
```
  void boundingBox(Circle c) {
      if (c instanceof Circle(Point(int x, int y), double radius)) {
```
That looks weird. An if whose condition always is right looks superfluous. It also makes it look as if one could write things such as
```
    if (c instanceof Circle(Point(int x, int y), double 1.0)) {
        …
    } else {
        …
    }
```
Finally, that code is wordy. I know that is the Java way, but couldn’t it be slightly shorter by not requiring specifying basic types as in
```
      if (c instanceof Circle(Point(x, y), radius)) {
```
? (I wouldn’t go as far as
```
      if (c instanceof Circle((x, y), radius)) {
```
. That doesnt feel Java to me)
$mfiguiere 7 hours ago
TLDR
* Destructuring via Record Patterns
The most prominent feature is the ability to use a record pattern on the left-hand side of a local variable declaration. This allows you to "destructure" an object and initialize multiple variables in a single statement.
Traditional way:
```
  Point p = getPoint();
  int x = p.x();
  int y = p.y();
```
Enhanced way:
```
  Point(int x, int y) = getPoint();
```
This also supports nested patterns, allowing you to reach deep into an object hierarchy in one go:
```
  Circle(Point(int x, int y), double radius) = getCircle();
```
* Pattern Matching in Enhanced for Loops
You can now use these same record patterns in the header of an enhanced for loop to extract data from every element in a collection or array.
```
  for (Circle(Point(int x, int y), double radius) : circles) {
      // Directly use x, y, and radius here
  }
```