Example 1: Join Two Lists using addAll()
import java.util.ArrayList;
import java.util.List;
public class JoinLists {
public static void main(String[] args) {
List<String> list1 = new ArrayList<String>();
list1.add("a");
List<String> list2 = new ArrayList<String>();
list2.add("b");
List<String> joined = new ArrayList<String>();
joined.addAll(list1);
joined.addAll(list2);
System.out.println("list1: " + list1);
System.out.println("list2: " + list2);
System.out.println("joined: " + joined);
}
}
Output
list1: [a] list2: [b] joined: [a, b]
In the above program, we used List's addAll() method to join lists list1 and list2 to the joined list.
Example 2: Join Two Lists using union()
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.collections.ListUtils;
public class JoinLists {
public static void main(String[] args) {
List<String> list1 = new ArrayList<String>();
list1.add("a");
List<String> list2 = new ArrayList<String>();
list2.add("b");
List<String> joined = ListUtils.union(list1, list2);
System.out.println("list1: " + list1);
System.out.println("list2: " + list2);
System.out.println("joined: " + joined);
}
}
The output of this program is the same as Example 1.
In the above program, we used union() method to join the given lists to joined.
Example 3: Join Two Lists using stream
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class JoinLists {
public static void main(String[] args) {
List<String> list1 = new ArrayList<String>();
list1.add("a");
List<String> list2 = new ArrayList<String>();
list2.add("b");
List<String> joined = Stream.concat(list1.stream(), list2.stream())
.collect(Collectors.toList());
System.out.println("list1: " + list1);
System.out.println("list2: " + list2);
System.out.println("joined: " + joined);
}
}
The output of this program is the same as Example 1.
In the above program, we used Stream's concat() method to join two lists converted to streams. Then, we convert them back to List using toList().
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