Java中的AbstractList与示例

Java中的AbstractList类是Java Collection Framework 的一部分，实现了Collection 接口和AbstractCollection类。此类提供 List 接口的骨架实现，以最大限度地减少实现此接口所需的工作，该接口由Random Access数据存储（例如数组）支持。对于顺序访问数据（如链表），应优先使用 AbstractSequentialList 而非此类。

要实现一个不可修改的列表，只需要扩展这个 AbstractList 类并实现 get(int) 和 size() 方法。实现一个可修改的列表，为此额外覆盖 set​(int index, E element) 方法（否则将引发 UnsupportedOperationException）。如果列表是可变大小的，则应该覆盖 add(int, E) 和 remove(int) 方法。

类层次结构：

宣言：

public abstract class AbstractList extends AbstractCollection implements List

where E is the type of elements maintained by this collection.

构造函数： protected AbstractList() – 默认构造函数，但受到保护，它不允许创建 AbstractList 对象。

AbstractList al = new ArrayList();

示例 1： AbstractList 是一个抽象类，因此应为其分配一个子类的实例，例如 ArrayList、LinkedList 或 Vector。

Java

// Java code to illustrate AbstractList
import java.util.*;
  
public class AbstractListDemo {
    public static void main(String args[])
    {
  
        // Creating an empty AbstractList
        AbstractList list = new ArrayList();
  
        // Use add() method to add elements in the list
        list.add("Geeks");
        list.add("for");
        list.add("Geeks");
        list.add("10");
        list.add("20");
  
        // Displaying the AbstractList
        System.out.println("AbstractList:" + list);
    }
}

输出：

AbstractList:[Geeks, for, Geeks, 10, 20]

示例 2：

Java

// Java code to illustrate 
// methods of AbstractCollection 
  
import java.util.*; 
  
public class AbstractListDemo { 
    public static void main(String args[]) 
    { 
  
        // Creating an empty AbstractList 
        AbstractList 
            list = new LinkedList(); 
  
        // Using add() method to add elements in the list 
        list.add("Geeks"); 
        list.add("for"); 
        list.add("Geeks"); 
        list.add("10"); 
        list.add("20"); 
  
        // Output the list 
        System.out.println("AbstractList: " + list); 
  
        // Remove the head using remove() 
        list.remove(3); 
  
        // Print the final list 
        System.out.println("Final AbstractList: " + list); 
  
        // getting the index of last occurence 
        // using lastIndexOf() method 
        int lastindex = list.lastIndexOf("A"); 
  
        // printing the Index 
        System.out.println("Last index of A : "
                        + lastindex); 
    } 
} 

输出：

AbstractList: [Geeks, for, Geeks, 10, 20]
Final AbstractList: [Geeks, for, Geeks, 20]
Last index of A : -1

AbstractList 中的方法

METHOD	DESCRIPTION
add​(int index, E element)	Inserts the specified element at the specified position in this list (optional operation).
add​(E e)	Appends the specified element to the end of this list (optional operation).
addAll​(int index,  Collection c)	Inserts all of the elements in the specified collection into this list at the specified position (optional operation).
clear()	Removes all of the elements from this list (optional operation).
equals​(Object o)	Compares the specified object with this list for equality.
get​(int index)	Returns the element at the specified position in this list.
hashCode()	Returns the hash code value for this list.
indexOf​(Object o)	Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
iterator()	Returns an iterator over the elements in this list in proper sequence.
lastIndexOf​(Object o)	Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
listIterator()	Returns a list iterator over the elements in this list (in proper sequence).
listIterator​(int index)	Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.
remove​(int index)	Removes the element at the specified position in this list (optional operation).
removeRange​(int fromIndex, int toIndex)	Removes from this list all of the elements whose index is between fromIndex, inclusive, and toIndex, exclusive.
set​(int index, E element)	Replaces the element at the specified position in this list with the specified element (optional operation).
subList​(int fromIndex, int toIndex)	Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive.

在类Java.util.AbstractCollection 中声明的方法

METHOD	DESCRIPTION
addAll​(Collection c)	Adds all of the elements in the specified collection to this collection (optional operation).
contains​(Object o)	Returns true if this collection contains the specified element.
containsAll​(Collection c)	Returns true if this collection contains all of the elements in the specified collection.
isEmpty()	Returns true if this collection contains no elements.
remove​(Object o)	Removes a single instance of the specified element from this collection, if it is present (optional operation).
removeAll​(Collection c)	Removes all of this collection’s elements that are also contained in the specified collection (optional operation).
retainAll​(Collection c)	Retains only the elements in this collection that are contained in the specified collection (optional operation).
toArray()	Returns an array containing all of the elements in this collection.
toArray​(T[] a)	Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
toString()	Returns a string representation of this collection.

在接口Java.util.Collection 中声明的方法

METHOD	DESCRIPTION
parallelStream()	Returns a possibly parallel Stream with this collection as its source.
removeIf​(Predicate filter)	Removes all of the elements of this collection that satisfy the given predicate.
stream()	Returns a sequential Stream with this collection as its source.
toArray​(IntFunction generator)	Returns an array containing all of the elements in this collection, using the  provided generator function to allocate the returned array.

在接口Java .util.List 中声明的方法

METHOD	DESCRIPTION
addAll​(Collection c)	Appends all of the elements in the specified collection to the end of this list, in the order that  they are returned by the specified collection’s iterator (optional operation).
contains​(Object o)	Returns true if this list contains the specified element.
containsAll​(Collection c)	Returns true if this list contains all of the elements of the specified collection.
isEmpty()	Returns true if this list contains no elements.
remove​(int index)	Removes the element at the specified position in this list (optional operation).
removeAll​(Collection c)	Removes from this list all of its elements that are contained in the specified collection (optional operation).
replaceAll​(UnaryOperator operator)	Replaces each element of this list with the result of applying the operator to that element.
retainAll​(Collection c)	Retains only the elements in this list that are contained in the specified collection (optional operation).
size()	Returns the number of elements in this list.
sort​(Comparator c)	Sorts this list according to the order induced by the specified Comparator.
spliterator()	Creates a Spliterator over the elements in this list.
toArray()	Returns an array containing all of the elements in this list in proper sequence (from first to last element).
toArray​(T[] a)	Returns an array containing all of the elements in this list in proper sequence (from first to last element) ; the runtime type of the returned array is that of the specified array.

参考： Java : Java