List的安全复制

import java.util.ArrayList;   
import java.util.Collections;   
import java.util.List;   
  
public class SafeListCopy extends Object {   
  public static void printWords(String[] word) {   
    System.out.println("word.length=" + word.length);   
    for (int i = 0; i < word.length; i++) {   
      System.out.println("word[" + i + "]=" + word[i]);   
    }   
  }   
  
  public static void main(String[] args) {   
    List wordList = Collections.synchronizedList(new ArrayList());   
  
    wordList.add("Synchronization");   
    wordList.add("is");   
    wordList.add("important");   
  
    String[] wordA = (String[]) wordList.toArray(new String[0]);   
  
    printWords(wordA);   
  
    String[] wordB;   
    synchronized (wordList) {   
      int size = wordList.size();   
      wordB = new String[size];   
      wordList.toArray(wordB);   
    }   
  
    printWords(wordB);   
  
    // Third technique (the 'synchronized' *is* necessary)   
    String[] wordC;   
    synchronized (wordList) {   
      wordC = (String[]) wordList.toArray(new String[wordList.size()]);   
    }   
  
    printWords(wordC);   
  }   
}