Apache Commons Collections - Bag Interface
New Interfaces are added to supports bags. A Bag defines a collection which counts the number of times an object appears in the collection. For example, if a Bag contains {a, a, b, c} then getCount("a") will return 2 while uniqueSet() returns the unique values.
Interface Declaration
Following is the declaration for org.apache.commons.collections4.Bag<E> interface −
public interface Bag<E>
extends Collection<E>
Methods
| Sr.No. | Method & Description |
|---|---|
| 1 |
boolean add(E object)
(Violation) Adds one copy of the specified object to the Bag.
|
| 2 |
boolean add(E object, int nCopies)
Adds nCopies copies of the specified object to the Bag.
|
| 3 |
boolean containsAll(Collection<?> coll)
(Violation) Returns true if the bag contains all elements in the given collection, respecting cardinality.
|
| 4 |
int getCount(Object object)
Returns the number of occurrences (cardinality) of the given object currently in the bag.
|
| 5 |
Iterator<E> iterator()
Returns an Iterator over the entire set of members, including copies due to cardinality.
|
| 6 |
boolean remove(Object object)
(Violation) Removes all occurrences of the given object from the bag.
|
| 7 |
boolean remove(Object object, int nCopies)
Removes nCopies copies of the specified object from the Bag.
|
| 8 |
boolean removeAll(Collection<?> coll)
(Violation) Remove all elements represented in the given collection, respecting cardinality.
|
| 9 |
boolean retainAll(Collection<?> coll)
(Violation) Remove any members of the bag that are not in the given collection, respecting cardinality.
|
| 10 |
int size()
Returns the total number of items in the bag across all types.
|
| 11 |
Set<E> uniqueSet()
Returns a Set of unique elements in the Bag.
|
Methods Inherited
This interface inherits methods from the following interface −
- java.util.Collection
Example of Bag Interface
BagTester.java
import org.apache.commons.collections4.Bag;
import org.apache.commons.collections4.bag.HashBag;
public class BagTester {
public static void main(String[] args) {
Bag<String> bag = new HashBag<>();
//add "a" two times to the bag.
bag.add("a" , 2);
//add "b" one time to the bag.
bag.add("b");
//add "c" one time to the bag.
bag.add("c");
//add "d" three times to the bag.
bag.add("d",3);
//get the count of "d" present in bag.
System.out.println("d is present " + bag.getCount("d") + " times.");
System.out.println("bag: " +bag);
//get the set of unique values from the bag
System.out.println("Unique Set: " +bag.uniqueSet());
//remove 2 occurrences of "d" from the bag
bag.remove("d",2);
System.out.println("2 occurences of d removed from bag: " +bag);
System.out.println("d is present " + bag.getCount("d") + " times.");
System.out.println("bag: " +bag);
System.out.println("Unique Set: " +bag.uniqueSet());
}
}
Output
It will print the following result.
d is present 3 times.
bag: [2:a,1:b,1:c,3:d]
Unique Set: [a, b, c, d]
2 occurences of d removed from bag: [2:a,1:b,1:c,1:d]
d is present 1 times.
bag: [2:a,1:b,1:c,1:d]
Unique Set: [a, b, c, d]