Google Guava 地图与 Java Util 地图

Question

在查看开源代码时，我多次遇到类似

的语句

Map<String, List<String>> map = Maps.newHashMap();

其中 Maps 属于软件包 com.google.common.collect.Maps (Google Guava)

为什么我们不能简单地使用标准：

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

代替？

Answer 1

这里的要点：在 Java 引入菱形运算符之前，您必须重复泛型类型参数，然后才能

Map<Whatever> myMap = new HashMap<Whatever>()

番石榴调用让您避免了重复Whatever。换句话说：这不过是一种无用（因此被弃用）的便捷方法，因为 Java 具有菱形运算符。它 JavaDoc clearly explains 那。

newHashMap

public static HashMap newHashMap()

…

Note for Java 7 and later: this method is now unnecessary and should be treated as deprecated. Instead, use the HashMap constructor directly, taking advantage of the new "diamond" syntax.

Answer 2

您的问题已由 JavaDoc 回答：

Note for Java 7 and later: this method is now unnecessary and should be treated as deprecated. Instead, use the HashSet constructor directly, taking advantage of the new "diamond" syntax.

Google Guava 地图与 Java Util 地图

Google Guava Maps vs Java Util Map

java

guava