Java集合框架入门教程

5星 · 超过95%的资源需积分: 16 53 浏览量更新于2024-07-31 收藏 351KB PDF 举报

"Java集合框架入门教程，涵盖了集合框架的基础、接口、类、特殊实现、历史、算法支持、使用问题及替代方案等" 在Java编程中，集合框架（Java Collections Framework）是一个至关重要的部分，它提供了一组接口和类，用于高效地存储、管理和操作数据。这本书针对初学者和有经验的开发者，通过简单的编程示例，引导读者快速掌握集合框架的核心概念。 1. **集合框架概述** 集合框架是Java SE API的重要组成部分，它包含一系列接口和类，如List、Set、Queue和Map，它们提供了处理对象集合的方法。这个框架使得数据操作更加简洁，提高了代码的可读性和可维护性。 2. **集合接口和类** - **List**: 有序的元素集合，允许重复元素，如ArrayList和LinkedList。 - **Set**: 不允许重复元素的集合，如HashSet、LinkedHashSet和TreeSet，它们根据不同的规则保证元素唯一性。 - **Map**: 存储键值对的数据结构，如HashMap、LinkedHashMap和TreeMap，其中键是唯一的。 - **Queue**: 代表先进先出（FIFO）的数据结构，如ArrayDeque和PriorityQueue。 3. **特殊集合实现** - **Concurrent Collections**: 例如ConcurrentHashMap和CopyOnWriteArrayList，它们提供了线程安全的操作，适合多线程环境。 - **Immutable Collections**: 如Collections.unmodifiableList()返回的不可变列表，防止集合被意外修改。 - **WeakReferences**: WeakHashMap使用弱引用，允许垃圾收集器回收不再被引用的对象。 4. **历史上的集合类** 早期的集合类，如Vector和Hashtable，由于线程安全但性能较低，逐渐被新版本的集合框架取代。了解它们的历史有助于理解框架的发展和改进。 5. **算法支持** 集合框架提供了诸如sort()、shuffle()、removeAll()等方法，实现了基本的算法操作，简化了开发者的任务。 6. **使用问题** 这一章节可能涉及遍历集合时的性能优化、迭代器的使用、容量规划以及如何选择合适的集合类型以避免内存溢出等问题。 7. **替代集合** 除了标准集合框架外，还有如Guava库提供的更高级的集合工具，如Multiset、Multimap和Immutable collections，这些工具提供了额外的功能和性能优势。 8. **练习与总结** 书中可能包含一系列练习题，帮助读者巩固所学知识，并在最后进行总结，回顾整个集合框架的关键点。通过学习这本书，读者不仅可以理解Java集合框架的基本原理，还能掌握如何在实际项目中有效利用这些工具，提升代码质量与效率。

override the behavior.

Collections Framework design concerns

In the creation of the Collections Framework, the Sun development team needed to provide

flexible interfaces that manipulated groups of elements. To keep the design simple, instead

of providing separate interfaces for optional capabilities, the interfaces define all the methods

an implementation class may provide. However, some of the interface methods are optional.

Because an interface implementation must provide implementations for all the interface

methods, there needed to be a way for a caller to know if an optional method is not

supported. The manner the framework development team chose to signal callers when an

optional method is called was to throw an UnsupportedOperationException. If in the

course of using a collection an UnsupportedOperationException is thrown, then the

operation failed because it is not supported. To avoid having to place all collection operations

within a try-catch block, the UnsupportedOperationException class is an extension

of the RuntimeException class.

In addition to handling optional operations with a run-time exception, the iterators for the

concrete collection implementations are fail-fast . That means that if you are using an

Iterator to traverse a collection while the underlying collection is being modified by

another thread, then the Iterator fails immediately by throwing a

ConcurrentModificationException (another RuntimeException). That means the

next time an Iterator method is called, and the underlying collection has been modified,

the ConcurrentModificationException exception gets thrown.

Set interface

The Set interface extends the Collection interface and, by definition, forbids duplicates

within the collection. All the original methods are present and no new methods are

introduced. The concrete Set implementation classes rely on the equals() method of the

object added to check for equality.

HashSet and TreeSet classes

The Collections Framework provides two general-purpose implementations of the Set

interface: HashSet and TreeSet. More often than not, you will use a HashSet for storing

your duplicate-free collection. For efficiency, objects added to a HashSet need to implement

the hashCode() method in a manner that properly distributes the hash codes. While most

system classes override the default hashCode() implementation in Object, when creating

Presented by developerWorks, your source for great tutorials

ibm.com/developerWorks

Java Collections Framework Page 8

your own classes to add to a HashSet remember to override hashCode(). The TreeSet

implementation is useful when you need to extract elements from a collection in a sorted

manner. In order to work properly, elements added to a TreeSet must be sortable. The

Collections Framework adds support for Comparable elements and will be covered in detail

in "Comparable interface" in Sorting on page 17. For now, just assume a tree knows how to

keep elements of the java.lang wrapper classes sorted. It is generally faster to add

elements to a HashSet, then convert the collection to a TreeSet for sorted traversal.

To optimize HashSet space usage, you can tune the initial capacity and load factor. The

TreeSet has no tuning options, as the tree is always balanced, ensuring log(n)

performance for insertions, deletions, and queries.

Both HashSet and TreeSet implement the Cloneable interface.

Set usage example

To demonstrate the use of the concrete Set classes, the following program creates a

HashSet and adds a group of names, including one name twice. The program then prints

out the list of names in the set, demonstrating the duplicate name isn't present. Next, the

program treats the set as a TreeSet and displays the list sorted.

import java.util.*;

public class SetExample {

public static void main(String args[]) {

Set set = new HashSet();

set.add("Bernadine");

set.add("Elizabeth");

set.add("Gene");

set.add("Elizabeth");

set.add("Clara");

System.out.println(set);

Set sortedSet = new TreeSet(set);

System.out.println(sortedSet);

}

Running the program produces the following output. Notice that the duplicate entry is only

present once, and the second list output is sorted alphabetically.

[Gene, Clara, Bernadine, Elizabeth]

[Bernadine, Clara, Elizabeth, Gene]

AbstractSet class

The AbstractSet class overrides the equals() and hashCode() methods to ensure

two equal sets return the same hash code. Two sets are equal if they are the same size and

contain the same elements. By definition, the hash code for a set is the sum of the hash

codes for the elements of the set. Thus, no matter what the internal ordering of the sets, two

equal sets will report the same hash code.

Exercises

Presented by developerWorks, your source for great tutorials

ibm.com/developerWorks

Java Collections Framework Page 9

剩余43页未读，继续阅读

cvison

粉丝: 3
资源: 2

Java集合框架入门教程

Java Collections.pdf

Java6 Collection Framework 新特性概览.pdf

请帮我讲解一下JAVA中的collection framework

java判断list是否为空,用那个工具类？

怎么用java实现红黑树

linkedhashmap hashmap

我现在有一个场景，有一个list集合，现在我需要对这个集合进行分页后返回给调用方，用java应该怎么实现

设计模式（迭代器模式）

LinkedHashMap

LinkedList主要实现类

最新资源