创建不同对象的实例列表 [英] Creating instance list of different objects

问题描述

我正试图创建一个包含不同类实例的arraylist.如何在不定义类类型的情况下创建列表? (<Employee>)

I'm tring to create an arraylist of different class instances. How can I create a list without defining a class type? (<Employee>)

List<Employee> employees = new ArrayList<Employee>();
employees.add(new Employee());
Employee employee = employees.get(0);

推荐答案

您可以创建对象列表，例如List<Object> list = new ArrayList<Object>().由于所有类的实现都从java.lang.Object类隐式或显式扩展，因此该列表可以容纳任何对象，包括Employee，Integer，String等的实例.

You could create a list of Object like List<Object> list = new ArrayList<Object>(). As all classes implementation extends implicit or explicit from java.lang.Object class, this list can hold any object, including instances of Employee, Integer, String etc.

从此列表中检索元素时，将检索Object而不是Employee，这意味着在这种情况下，您需要执行以下显式强制转换:

When you retrieve an element from this list, you will be retrieving an Object and no longer an Employee, meaning you need to perform a explicit cast in this case as follows:

List<Object> list = new ArrayList<Object>();
list.add("String");
list.add(Integer.valueOf(1));
list.add(new Employee());

Object retrievedObject = list.get(2);
Employee employee = (Employee)list.get(2); // explicit cast

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