Java: split a List into two sub-Lists?

Question

What\'s the simplest, most standard, and/or most efficient way to split a List into two sub-Lists in Java? It\'s OK to mutate the original List, so no copying should be nece

Answer 1

import java.util.Collection;

public class CollectionUtils {

  /**
   * Will split the passed collection so that the size of the new collections
   * is not greater than maxSize
   * @param t
   * @param maxSize
   * @return a List containing splitted collections
   */

  @SuppressWarnings("unchecked")
  public static  List>split(Collection t, int maxSize) {
    int counter = 0;
    List> ret = new LinkedList>();
    Iteratoritr = t.iterator();
    try {
      Collection tmp = t.getClass().newInstance();
      ret.add(tmp);
      while(itr.hasNext()) {
        tmp.add(itr.next());
        counter++;
        if(counter>=maxSize && itr.hasNext()) {
          tmp = t.getClass().newInstance();
          ret.add(tmp);
          counter=0;
        }
      }
    } catch(Throwable e) {
      Logger.getLogger(CollectionUtils.class).error("There was an error spliting "+t.getClass(),e);
    }
    return ret;
  }

}

// JUnit test cases

import java.util.ArrayList;

/**
 *
 * $Change$
 * @version $Revision$
 * Last modified date & time $DateTime$
 */
public class CollectionUtilsTest {

  @Test
  public void testSplitList() {
    Listtest = new ArrayList(100);
    for (int i=1;i<101;i++) {
      test.add(i);
    }
    List> tests = CollectionUtils.split(test, 10);
    Assert.assertEquals("Size mismatch", 10,tests.size());

    TreeSet tmp = new TreeSet();
    for(Collection cs:tests) {
      for(Integer i:cs) {
        Assert.assertFalse("Duplicated item found "+i,tmp.contains(i));
        tmp.add(i);
      }
      System.out.println(cs);
    }
    int why = 1;
    for(Integer i:tmp) {
      Assert.assertEquals("Not all items are in the collection ",why,i.intValue());
      why++;
    }
  }
  @Test
  public void testSplitSet() {
    TreeSettest = new TreeSet();
    for (int i=1;i<112;i++) {
      test.add(i);
    }
    List> tests = CollectionUtils.split(test, 10);
    Assert.assertEquals("Size mismatch", 12,tests.size());

    TreeSet tmp = new TreeSet();
    int cI = 0;
    for(Collection cs:tests) {
      for(Integer i:cs) {
        Assert.assertFalse("Duplicated item found "+i,tmp.contains(i));
        tmp.add(i);
      }
//      if(cI>10) {
        System.out.println(cs);
//      }
      cI++;
    }
    int why = 1;
    for(Integer i:tmp) {

      Assert.assertEquals("Not all items are in the collection ",why,i.intValue());
      why++;
    }
  }
}