Collection接口是构建收集框架的基础。它声明了所有集合将拥有的核心方法。下表总结了这些方法。
| Sr.No. | Method & Remark |
|---|---|
| 1 |
boolean add(Object obj) 将obj添加到调用集合中。如果将obj添加到集合中，则返回true。如果obj已经是集合的成员，或者该集合不允许重复，则返回false。 |
| 2 |
boolean addAll(Collection c) 将c的所有元素添加到调用集合中。 |
| 3 |
void clear() 从调用集合中删除所有元素。 |
| 4 |
boolean contains(Object obj) 如果obj是调用集合的元素，则返回true。否则，返回false。 |
| 5 |
boolean containsAll(Collection c) 如果调用集合包含 c 的所有元素，则返回true。否则，返回false。 |
| 6 |
boolean equals(Object obj) 如果调用集合和obj相等，则返回true。否则，返回false。 |
| 7 |
int hashCode() 返回调用集合的hashCode。 |
| 8 |
boolean isEmpty() 如果调用集合为空，则返回true。否则，返回false。 |
| 9 |
Iterator iterator() 返回调用集合的迭代器。 |
| 10 |
boolean remove(Object obj) 从调用集合中删除obj的一个。如果该元素已删除，则返回true。否则，返回false。 |
| 11 |
boolean removeAll(Collection c) 从调用集合中删除c的所有元素。如果集合发生更改(即元素已删除)，则返回true。否则，返回false。 |
| 12 |
boolean keepAll(Collection c) 从调用集合中除去c中的所有元素。如果集合发生更改(即元素已删除)，则返回true。否则，返回false。 |
| 13 |
int size() 返回调用集合中保留的元素数。 |
| 14 |
Object[] toArray() 返回一个数组，其中包含调用集合中存储的所有元素。数组元素是集合元素的副本。 |
| 15 |
Object [] toArray(Object array []) 返回一个仅包含类型与数组类型匹配的集合元素的数组。 |
Collection 示例
以下是一个示例，说明上述收集方法的各种类实现中的几种方法-
import java.util.*;
public class CollectionsDemo {
public static void main(String[] args) {
//数组列表
List a1 = new ArrayList();
a1.add("Learnfk");
a1.add("Mahnaz");
a1.add("Ayan");
System.out.println(" ArrayList Elements");
System.out.print("\t" + a1);
</span><span class="com">//链表</span><span class="pln">
</span><span class="typ">List</span><span class="pln"> l1 </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">LinkedList</span><span class="pun">();</span><span class="pln">
l1</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="str">"Learnfk"</span><span class="pun">);</span><span class="pln">
l1</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="str">"Mahnaz"</span><span class="pun">);</span><span class="pln">
l1</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="str">"Ayan"</span><span class="pun">);</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">();</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">" LinkedList Elements"</span><span class="pun">);</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"\t"</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> l1</span><span class="pun">);</span><span class="pln">
</span><span class="com">//哈希集</span><span class="pln">
</span><span class="typ">Set</span><span class="pln"> s1 </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">HashSet</span><span class="pun">();</span><span class="pln">
s1</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="str">"Learnfk"</span><span class="pun">);</span><span class="pln">
s1</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="str">"Mahnaz"</span><span class="pun">);</span><span class="pln">
s1</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="str">"Ayan"</span><span class="pun">);</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">();</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">" Set Elements"</span><span class="pun">);</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"\t"</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> s1</span><span class="pun">);</span><span class="pln">
</span><span class="com">//哈希映射</span><span class="pln">
</span><span class="typ">Map</span><span class="pln"> m1 </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">HashMap</span><span class="pun">();</span><span class="pln">
m1</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"Learnfk"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"8"</span><span class="pun">);</span><span class="pln">
m1</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"Mahnaz"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"31"</span><span class="pun">);</span><span class="pln">
m1</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"Ayan"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"12"</span><span class="pun">);</span><span class="pln">
m1</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"Daisy"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"14"</span><span class="pun">);</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">();</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">" Map Elements"</span><span class="pun">);</span><span class="pln">
</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"\t"</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> m1</span><span class="pun">);</span><span class="pln">
}
}
这将产生以下输出-
ArrayList Elements [Learnfk, Mahnaz, Ayan] LinkedList Elements [Learnfk, Mahnaz, Ayan] Set Elements [Ayan, Learnfk, Mahnaz] Map Elements {Daisy=14, Ayan=12, Learnfk=8, Mahnaz=31}
