Tóm Tắt
Set interface:
A set represents a group of elements which can’t contain a duplicate element. It extends the collection interface.
Note: Set interface contains only methods inherited from Collection interface and adds the restriction that can’t contain a duplicate element.
Commonly Used methods of Set interface:
1. add(Object obj): Add object to the calling collection. It returns true if collection changed after this call otherwise returns false.
Syntax: public boolean add(Object obj)
2. addAll(Collection c): Add all objects to the calling collection. It returns true if collection changed after this call otherwise returns false.
Syntax: public boolean addAll(Collection c)
3. clear(): Remove all elements from the calling collection.
Syntax: public void clear()
4. contains(Object obj): It returns true if this collection contains the specified object otherwise returns false.
Syntax: public boolean contains(Object obj)
5. containsAll(Collection c):It returns true if this collection contains all elements of the specified collection otherwise returns false.
Syntax: public boolean containsAll(Collection c)
6. equals(Object obj): It returns true if this collection equals to the specified object otherwise returns false.
Syntax: public boolean equals(Object obj)
7. hashCode(): It returns the hash code of the calling collection.
Syntax: public int hashCode()
8. isEmpty(): It returns true if the calling collection is empty otherwise returns false.
Syntax: public boolean isEmpty()
9. iterator(): It returns an iterator instance for the calling collection.
Syntax: public Iterator iterator()
10. remove(Object obj): It remove the specified object from the calling collection. It returns true if collection changed after this call otherwise returns false.
Syntax: public boolean remove(Object obj)
11. removeAll(Collection c): It remove all elements of the specified collection from the calling collection. It returns true if collection changed after this call otherwise returns false.
Syntax: public boolean removeAll(Collection c)
12. retainAll(Collection c): It remove all elements except those of the specified collection from the calling collection. It returns true if collection changed after this call otherwise returns false.
Syntax: public boolean retainAll(Collection c)
13. size(): It returns the number of elements in the calling collection.
Syntax: public int size()
14. toArray( ): It returns an array of containing all elements of the calling collection.
Syntax: public Object[ ] toArray()
A simple example of HashSet class to explain few methods of Set interface.
HashSetTest.java
import
java.util.HashSet
;
import
java.util.Iterator
;
import
java.util.Set
;
/** * This class is used to show the HashSet functionality. * @author w3spoint */
public
class
HashSetTest{
public
static
void
main(
String
args[
]
)
{
//Create HashSet object.
Set
hashSet=
new
HashSet
(
)
;
//Add objects to the HashSet.
hashSet.add
(
"Roxy"
)
;
hashSet.add
(
"Sunil"
)
;
hashSet.add
(
"Sandy"
)
;
hashSet.add
(
"Munish"
)
;
hashSet.add
(
"Pardeep"
)
;
//Print the HashSet object.
System
.out
.println
(
"HashSet elements:"
)
;
System
.out
.println
(
hashSet)
;
//Print the HashSet elements using iterator.
Iterator
iterator=
hashSet.iterator
(
)
;
System
.out
.println
(
"HashSet elements using iterator:"
)
;
while
(
iterator.hasNext
(
)
)
{
System
.out
.println
(
iterator.next
(
)
)
;
}
}
}
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set; /**
* This class is used to show the HashSet functionality.
* @author w3spoint
*/
public class HashSetTest {
public static void main(String args[]){
//Create HashSet object.
Set hashSet = new HashSet();
//Add objects to the HashSet.
hashSet.add(“Roxy”);
hashSet.add(“Sunil”);
hashSet.add(“Sandy”);
hashSet.add(“Munish”);
hashSet.add(“Pardeep”);
//Print the HashSet object.
System.out.println(“HashSet elements:”);
System.out.println(hashSet);
//Print the HashSet elements using iterator.
Iterator iterator=hashSet.iterator();
System.out.println(“HashSet elements using iterator:”);
while(iterator.hasNext()){
System.out.println(iterator.next());
}
}
}
Output:
HashSet
elements:
[
Sandy, Pardeep, Munish, Sunil, Roxy]
HashSet
elements using iterator:
Sandy Pardeep Munish Sunil Roxy
HashSet elements:
[Sandy, Pardeep, Munish, Sunil, Roxy]
HashSet elements using iterator:
Sandy
Pardeep
Munish
Sunil
Roxy
Download this example.
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