java - 初始化 map > - Java 7

Question

我需要初始化一个like Map x<Apartment,Vector<Expense>>如果我 @override 它允许我 map 方法

Description Resource    Path    Location    Type
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.isEmpty()   Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.size()  Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.keySet()    Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.remove(Object)  Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.entrySet()  Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.putAll(Map<? extends Apartment,? extends Vector<Expense>>)  Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.values()    Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.clear() Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.get(Object) Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.containsKey(Object) Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.containsValue(Object)   Repository.java /proj_individual/src/repo   line 12 Java Problem
The type new Map<Apartment,Vector<Expense>>(){} must implement the inherited abstract method Map<Apartment,Vector<Expense>>.put(Apartment, Vector<Expense>) Repository.java /proj_individual/src/repo   line 12 Java Problem

但是我在网上看到 Map 不是一个接口(interface)，它是一个类，我是不是做错了，还是必须这样做？

Answer 1

Map<Apartment, Vector<Expense>> map = new HashMap<Apartment, Vector<Expense>>();

Map 是一个接口(interface)(如 the javadoc 所说 — javadoc 应该是您的引用，而不是 Internet)。您需要选择一个实现(HashMap 是最常用的实现，但还有其他实现，具有其他特性)。

您还应该忘掉 Vector。它不应该再被使用了。使用 List 作为类型，ArrayList 作为实现(还有其他 List 实现，但 ArrayList 几乎总是你想要的):

Map<Apartment, List<Expense>> map = new HashMap<Apartment, List<Expense>>();

或者只是

Map<Apartment, List<Expense>> map = new HashMap<>();

如果您使用的是 Java 7。