使用Groovy和Java中的自定義鍵映射

Question

我想在Groovy中使用映射，其中鍵將是不可變類的實例。

這是我在Java中經常這樣做，它工作正常，就像這個例子類：

public class TestMap { 
    static final class Point { 
     final int x; final int y; 
     public Point(int x, int y) {this.x = x;this.y = y;} 
    } 

    public static void main(String[] args) { 
     Map<Point, String> map = new HashMap<>(); 
     final Point origin = new Point(0, 0); 
     map.put(origin, "hello world !"); 
     if(!map.containsKey(origin)) 
      throw new RuntimeException("can't find key origin in the map"); 
     if(!map.containsKey(new Point(0,0))) { 
      throw new RuntimeException("can't find new key(0,0) in the map"); 
     } 
    } 
} 

但是當我嘗試實現使用Groovy同樣的事情，這是行不通的。 爲什麼？ 下面是使用Groovy樣本非工作示例：

class Point { 
    final int x; final int y 
    Point(int x, int y) { this.x = x; this.y = y } 
    public String toString() { return "{x=$x, y=$y}" } 
} 

def origin = new Point(0, 0) 
def map = [(origin): "hello"] 
map[(new Point(1,1))] = "world" 
map.put(new Point(2,2), "!") 

assert map.containsKey(origin) // this works: when it's the same ref 
assert map.containsKey(new Point(0,0)) 
assert map.containsKey(new Point(1,1)) 
assert map.containsKey(new Point(2,2)) 
assert !map.containsKey(new Point(3,3)) 

Answer 1

您必須對您的Point類的equals和hashCode方法，以便實例可以作爲按鍵在HashMap

你可以找到這很快通過在Groovy中添加註釋：

import groovy.transform.* 

@EqualsAndHashCode 
class Point { 
    final int x; final int y 
    Point(int x, int y) { this.x = x; this.y = y } 
    public String toString() { return "{x=$x, y=$y}" } 
}