Java List vs ArrayList [英] Java List vs ArrayList

问题描述

作为一个C ++老朋友，我已经设法解决了我的问题，但是我无法在此处将底层的Java机制包装起来：

 矢量<对象> x = new Vector< Object>（）; // OK 
 ArrayList< Object> y = new ArrayList< Object>（）; // OK 
 List< Object> zzz = new ArrayList< Object>（）; //好的解决了下面的问题，但问题依然存在
 List< Object> z = new List< Object>（）; //为什么？编译器错误：无法实例化
  

解决方案

List 是一个接口，有点像C ++中一些带有 = 0 方法的类。
$ b

但 ArrayList< T> inherits List< ; T> （或用Java术语来实现它），所以这些引用是赋值兼容的。

As a C++ oldtimer I have managed to solve my problem but I can not wrap my head around the underlying Java mechanisms here:

Vector<Object> x = new Vector<Object>();        // OK
ArrayList<Object> y = new ArrayList<Object>();  // OK
List<Object> zzz = new ArrayList<Object>();     // OK solves problem below but question remains
List<Object> z = new List<Object>();            // WHY? Compiler error: Cannot instantiate 

解决方案

List is an interface, somewhat like a class with some = 0 methods in C++. You can't instantiate it.

But ArrayList<T> "inherits" List<T> (or in Java terms, implements it), so those references are assignment-compatible.

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