Jakarta Commons Cookbook

5.20. Performing Set Operations

Problem

You need to perform set operations to find the union, intersection, disjunction, and difference of two collections.

Solution

Use one of four CollectionUtils methods to perform set operations—union( ), intersection( ), disjunction(), and subtract( ) . Example 5-19 demonstrates the use of these four methods with two Collections.

Example 5-19. Using CollectionUtils union( ), intersection( ), disjunction( ), and subtract( )

import java.util.*;

String[] arrayA = new String[] { "1", "2", "3", "3", "4", "5" };
String[] arrayB = new String[] { "3", "4", "4", "5", "6", "7" };

List a = Arrays.asList( arrayA );
List b = Arrays.asList( arrayB );

Collection union = CollectionUtils.union( a, b );
                  Collection intersection = CollectionUtils.intersection( a, b );
                  Collection disjunction = CollectionUtils.disjunction( a, b );
                  Collection subtract = CollectionUtils.subtract( a, b ); Collections.sort( union ); Collections.sort( intersection ); Collections.sort( disjunction ); Collections.sort( subtract ); System.out.println( "A: " + ArrayUtils.toString( a.toArray( ) ) ); System.out.println( "B: " + ArrayUtils.toString( b.toArray( ) ) ); System.out.println( "Union: " + ArrayUtils.toString( union.toArray( ) ) ); System.out.println( "Intersection: " + ArrayUtils.toString( intersection.toArray( ) ) ); System.out.println( "Disjunction: " + ArrayUtils.toString( disjunction.toArray( ) ) ); System.out.println( "Subtract: " + ArrayUtils.toString( subtract.toArray( ) ) ); ...