Java 集合 同步ArrayList

package beginnersbook.com;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Collections;

public class Details {

   public static void main(String a[]){
       List<String> syncal = 
         Collections.synchronizedList(new ArrayList<String>());

       //Adding elements to synchronized ArrayList
       syncal.add("Pen");
       syncal.add("NoteBook");
       syncal.add("Ink");

       System.out.println("Iterating synchronized ArrayList:");
       synchronized(syncal) {
       Iterator<String> iterator = syncal.iterator(); 
       while (iterator.hasNext())
          System.out.println(iterator.next());
       }
   }
}

Iterating synchronized ArrayList:
Pen
NoteBook
Ink

package beginnersbook.com;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.Iterator;

public class Details {

 public static void main(String a[]){
    CopyOnWriteArrayList<String> al = new CopyOnWriteArrayList<String>();

    //Adding elements to synchronized ArrayList
    al.add("Pen");
    al.add("NoteBook");
    al.add("Ink");

    System.out.println("Displaying synchronized ArrayList Elements:");
    //Synchronized block is not required in this method
    Iterator<String> iterator = al.iterator(); 
    while (iterator.hasNext())
       System.out.println(iterator.next());
  }
}

Displaying synchronized ArrayList Elements:
Pen
NoteBook
Ink