Question

即使我使用泛型，也会在Map中将多个对象存储为键。

ArrayList<String> fruitlist = new ArrayList<>();    
fruitlist.addAll(Arrays.asList("Apple", "Banana", "Grapes"));           
ArrayList<String> vegglist = new ArrayList<>();    
vegglist.addAll(Arrays.asList("Potato", "Squash", "Beans"));

Map<String, ArrayList<String>> productsMap = new HashMap<>();           
Allien a = new Allien(101, "John");  //creted sperated Allien class and constructor    
Predator p = new Predator(102, "Lisa"); // creted sperated Predator class and constructor           
productsMap.put(a, fruitlist); //compile time error change type a as String    
productsMap.put(p, vegglist);  // same error

请建议将多个对象作为键放在哪里我错了，

Answer 1

您已将Map键指定为字符串，但需要一个对象。你需要改变你的地图声明，如下所示

Map<Object, ArrayList<String>> productsMap = new HashMap<>();

Answer 2

要将对象用作HashMap中的键，关键对象必须覆盖 hashCode 和等于方法。

见下面的示例，它给出输出“这是人100”：

Hotel    Market   Desc      Date      Values
ABC      France   SUP HB    Jan16      158
ABC      France   SUP HB    Feb16       33
ABC      France   SUP AI    Jan16       35
ABC      France   SUP AI    Feb16        6
ABC      France   DLX HB    Jan16       27
ABC      France   DLX HB    Feb16       10

将对象存储为地图中的键

2 个答案: