Collection Interface是Collection Framework的基本根接口，定义了Collection Interface所有成员都必须使用的基本方法；集合框架，包括处理、操作和访问数据的各种方式，都基于此集合接口。
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java中的Collection接口位于java.util.Collection包中，定义了集合家族所有成员都需要实现的基本方法。
以下方法在集合接口中定义，所有集合框架都应该实现。
| Method Name | Method Description |
| boolean add(Object object) | This method adds the specified object to the collection calling this method. It returns true if the object was added to the collection otherwise returns false if the object is already a part of the collection or if the collection does not allow duplicates elements. |
| boolean addAll(Collection collection) | This method adds all the elements of the specified collection to the collection calling this method. It returns true if the addition is successful, otherwise, it returns false. |
| boolean contains(Object object) | This method returns true if the specified object is a part of the collection calling this method; otherwise, it returns false. |
| void clear( ) | This method removes all elements from the collection calling this method. |
| boolean containsAll(Collection collection) | This method returns true if the collection calling this method contains all specified collection elements; otherwise, it returns false. |
| boolean equals(Object object) | This method returns true if the collection calling this method and the specified object are equal; otherwise, it returns false. |
| int hashCode( ) | This method returns the hash code for the collection calling this method. |
| boolean isEmpty( ) | This method returns true if the collection calling this method contains no elements; otherwise, it returns false. |
| Iterator iterator( ) | This method returns an iterator for the collection calling this method. |
| boolean remove(Object object) | This method removes the specified object from the collection calling this method. Returns true if the specified object was removed, otherwise returns false. |
| boolean removeAll(Collection collection) | This method removes all elements available in a specified collection from the collection calling this method. Returns true if there is a change in collection calling this method; otherwise, it returns false. |
| boolean retainAll(Collection collection) | This method removes all elements from the collection calling this method except those available in the specified collection. This method returns true if there is a change in collection calling this method; otherwise, it returns false. |
| int size( ) | This method returns the number of elements available in the collection calling this method. |
| Object[ ] toArray( ) | This method returns an array that contains all the elements stored in the collection calling this method. The array elements are, in fact, copies of the elements available in the calling collection. |
| Object[ ] toArray(Object array[ ]) | This method returns an array containing only those collection elements of the calling collection whose type matches the type of elements in the specified array. |
下面给出了 Java 中集合接口的示例：
在这个例子中，我们将展示java中集合接口的方法。我们将看到如何使用 add、addAll 和 size 方法。
代码：
package com.edubca.nonprimitivedemo;
// import collections
import java.util.ArrayList;
import java.util.List;
public class DataTypeDemo {
public static void main(String[] args) {
List arraylist1 = new ArrayList();
// Adding elements to arraylist
arraylist1.add("Yash");
arraylist1.add("Montu");
arraylist1.add("Ketan");
System.out.println(" ArrayList1 Elements are :");
System.out.println("\t" + arraylist1);
//printing size of arraylist1
System.out.println("Size of ArrayList1 is " +arraylist1.size() );
List arraylist2 = new ArrayList();
// Adding elements to arraylist
arraylist2.add("Chetan");
arraylist2.add("Chirag");
arraylist2.add("Ali");
System.out.println();
System.out.println(" ArrayList2 Elements are :");
System.out.println("\t" + arraylist2);
//printing size of arraylist2
System.out.println("Size of ArrayList1 is " +arraylist2.size() );
System.out.println();
// Adding elements of both lists to list1
arraylist1.addAll(arraylist2);
// Now Printing modified list
System.out.println(" ArrayList1 Elements after merging with ArrayList2 are : ");
System.out.println("\t" + arraylist1);
//printing size of arraylist1
System.out.println("Size of ArrayList1 is " +arraylist1.size() );
}
}输出：
在这个例子中，我们将看到更多集合接口的方法。
代码：
package com.edubca.nonprimitivedemo;
// import collections
import java.util.ArrayList;
import java.util.List;
// importing iterator
import java.util.Iterator;
public class DataTypeDemo {
public static void main(String[] args) {
// creating array list of type string
ArrayList<String> arraylist1 = new ArrayList<String>();
arraylist1.add("Spark");
arraylist1.add("Hadoop");
arraylist1.add("Hive");
arraylist1.add("Kafka");
System.out.println("Elements of list1 are : " + arraylist1);
ArrayList<String> arraylist2 = new ArrayList<String>();
arraylist2.add("Spark");
arraylist2.add("Hadoop");
arraylist2.add("Hive");
arraylist2.add("Kafka");
boolean isequal=arraylist1.equals(arraylist2); // check if both lists are equal
System.out.println("Elements of list2 are : " + arraylist2);
System.out.println ("Are Both Lists equal? " + isequal);
arraylist1.addAll(arraylist2); // merging both lists
// iterating arraylist
Iterator it=arraylist1.iterator();
System.out.println("Iterating Elements of Arraylist:");
while(it.hasNext()){
System.out.println(it.next());
}
}
}输出：
上面的文章让我们清楚地了解了java中的集合接口以及集合接口中可用的不同方法。上面介绍的 Java 代码示例展示了集合家族的成员如何使用集合接口的方法。
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