比较Iterator和ListIterator

最新推荐文章于 2024-11-04 18:18:56 发布

最新推荐文章于 2024-11-04 18:18:56 发布 · 99 阅读

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本文通过一个具体的Java程序对比了Iterator和ListIterator在遍历集合时的性能差异。通过对一万条记录的读取操作进行计时，展示了不同类型的迭代器在实际应用中的效率表现。

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import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;

/**
* compare iterator efficiency.
* @author sailing
* Date: 2007-10-01
*/
public final class CompareIterator {
/**
* define instance as single.
*/
     private static CompareIterator instance = new CompareIterator();
/**
* construct CompareIterator class.
*/
private CompareIterator() {
}
    /**
     * get single.
     * @return instance
     */
public static CompareIterator getInstance() {
  return instance;
}
/**
* init data.
* @return list
*/
private List initData() {
  List list = new ArrayList();
  Map map = null;
  int size = 10000;
  for(int i = 0; i < size; i++) {
   map = new HashMap();
   map.put("key"+i, "value"+2*i);
   list.add(map);
  }
  return list;
}
/**
* get system current time.
* @return time
*/
private Long getCurrentTime(){
  Long time = 0l;
  time = System.currentTimeMillis();
  return time;
}
/**
* read by iterator.
* @param list
*/
private void readByIterator(List list) {
  Iterator it = (Iterator) list.iterator();
  Map map = null;
  while(it.hasNext()){
   map = (HashMap) it.next();
  }
  System.out.println("ReadByIterator End.");
}
/**
* read by list iterator.
* @param list list
*/
    private void readByListIterator(List list) {
  ListIterator li = list.listIterator();
  Map map = null;
  while(li.hasNext()){
   map = (HashMap) li.next();
  }
  System.out.println("ReadByListIterator End.");
}
    /**
     * main.
     * @param args
     */
    public static void main(String []args) {
  CompareIterator ci = new CompareIterator();
  List list = ci.initData();
  long startTime1 = 0;
  long startTime2 = 0;
  long endTime1 = 0;
  long endTime2 = 0;

  startTime1 = ci.getCurrentTime();
  ci.readByIterator(list);
  endTime1 = ci.getCurrentTime();

  startTime2 = ci.getCurrentTime();
  ci.readByListIterator(list);
  endTime2 = ci.getCurrentTime();

  System.out.println("ReadByIterator Need Time: " + (endTime1 - startTime1));
  System.out.println("ReadByListIterator Need Time: " + (endTime2 - startTime2));

}
}