创建不同对象的实例列表 [英] Creating instance list of different objects
问题描述
我正在尝试创建不同类实例的数组列表.如何在不定义类类型的情况下创建列表?(<员工>)
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
你可以像List.由于所有类的实现都是从 java.lang.Object 类中隐式或显式扩展而来的，这个列表可以包含任何对象，包括 Employee、Integer 的实例, String 等
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.
当您从此列表中检索元素时，您将检索一个 Object 而不再是 Employee，这意味着在这种情况下您需要执行显式转换为如下:
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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