如何有效遍历集合中的对象
今天看了看practical java 中不要使用enumeration 或者iteration来便利对象，自己亲自试了一下，发现
如果如果针对小的数据集，效率问题不是很明显，对于大的数据集还有有一些差距的。由测试结果可以看出虽然loop
类比其他遍历方法少用一次查询方法，但是对于小的数据集，其结果比其他的遍历方法还要慢，但数据集越大loop的
优势越明显。
1. 对应的log类
package com.tn.app.log;
public class Log {
private long startmemory;
private long starttime;
private static Log log;
private Log() {
super();
}
public static Log getInstance() {
if (log == null)
log = new Log();
return log;
}
private void setStartMemory() {
Runtime runtime = Runtime.getRuntime();
runtime.gc();
startmemory = runtime.totalMemory() - runtime.freeMemory();
}
private void SetStartTime() {
starttime = System.currentTimeMillis();
}
public void start() {
SetStartTime();
setStartMemory();
}
public void end() {
setEndMemory();
SetEndTime();
}
private void setEndMemory() {
Runtime runtime = Runtime.getRuntime();
runtime.gc();
long endMemory = runtime.totalMemory() - runtime.freeMemory();
System.out.println("the consumed memory is"
+ Math.abs((endMemory - startmemory)));
}
private void SetEndTime() {
long endTime = System.currentTimeMillis();
System.out.println("the consumed time is" + (endTime - starttime));
System.out.println("===================================");
}
}
2. 对用的反射类
package com.tn.refector;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import com.tn.app.log.Log;
import com.tn.list.Total;
public class ListRefector implements InvocationHandler {
private Total total;
private Log log;
public ListRefector(Total targetCreator) {
this.total = targetCreator;
}
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
log = Log.getInstance();
log.start();
Object result = method.invoke(this.total, args);
log.end();
return result;
}
@SuppressWarnings("unchecked")
public static Object getListCreator(Total target) {
System.out.println("class name is " + target.toString());
Class targetClass = target.getClass();
ClassLoader loader = targetClass.getClassLoader();
Class[] interfaces = targetClass.getInterfaces();
ListRefector handler = new ListRefector(target);
return Proxy.newProxyInstance(loader, interfaces, handler);
}
}
3.实现类
package com.tn.list;
import java.util.Vector;
public interface Total {
int getTotal(Vector<Integer> vec);
}
package com.tn.list;
import java.util.Vector;
public class Loop implements Total {
public int getTotal(Vector<Integer> vec) {
int total = 0;
int size = vec.size();
for (int vecIndex = 0; vecIndex < size; vecIndex++) {
total += vec.get(vecIndex).intValue();
}
return total;
}
}
package com.tn.list;
import java.util.ListIterator;
import java.util.Vector;
public class ListIter implements Total {
public int getTotal(Vector<Integer> vec) {
int total = 0;
ListIterator<Integer> listInte = vec.listIterator();
while (listInte.hasNext())
total += ((Integer) (listInte.next())).intValue();
return total;
}
}
package com.tn.list;
import java.util.Iterator;
import java.util.ListIterator;
import java.util.Vector;
public class Iter implements Total {
public int getTotal(Vector<Integer> vec) {
int total = 0;
Iterator<Integer> itera = vec.iterator();
while (itera.hasNext())
total += ((Integer) (itera.next())).intValue();
return total;
}
}
package com.tn.list;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.ListIterator;
import java.util.Vector;
public class Enume implements Total {
public int getTotal(Vector<Integer> vec) {
int total = 0;
Enumeration<Integer> enume = vec.elements();
while (enume.hasMoreElements())
total += ((Integer) (enume.nextElement())).intValue();
return total;
}
}
4. 测试类
package com.tn.refector;
import java.util.Vector;
import com.tn.list.Enume;
import com.tn.list.Iter;
import com.tn.list.ListIter;
import com.tn.list.Loop;
import com.tn.list.Total;
public class Dynamic {
private static Total target, proxy;
public static void main(String[] args) {
Vector<Integer> vec = InitVec(2000000);
getTotalByEnum(vec);
getTotalByIter(vec);
getTotalByListIter(vec);
getTotalByLoop(vec);
}
private static void getTotalByLoop(Vector<Integer> vec) {
target = new Loop();
proxy = (Total) ListRefector.getListCreator(target);
proxy.getTotal(vec);
}
private static void getTotalByListIter(Vector<Integer> vec) {
target = new ListIter();
proxy = (Total) ListRefector.getListCreator(target);
proxy.getTotal(vec);
}
private static void getTotalByIter(Vector<Integer> vec) {
target = new Iter();
proxy = (Total) ListRefector.getListCreator(target);
proxy.getTotal(vec);
}
private static void getTotalByEnum(Vector<Integer> vec) {
target = new Enume();
proxy = (Total) ListRefector.getListCreator(target);
proxy.getTotal(vec);
}
private static Vector<Integer> InitVec(int size) {
Vector<Integer> vec = new Vector<Integer>();
for (int startIndex = 0; startIndex < size; startIndex++) {
vec.add(startIndex);
}
return vec;
}
}
5. 结果如下：
当size =100000
class name is com.tn.list.Enume@757aef
the consumed memory is56
the consumed time is15
===================================
class name is com.tn.list.Iter@61de33
the consumed memory is16
the consumed time is31
===================================
class name is com.tn.list.ListIter@ca0b6
the consumed memory is16
the consumed time is31
===================================
class name is com.tn.list.Loop@1a758cb
the consumed memory is16
the consumed time is32
===================================
当size= 100
class name is com.tn.list.Enume@757aef
the consumed memory is56
the consumed time is16
===================================
class name is com.tn.list.Iter@61de33
the consumed memory is488
the consumed time is15
===================================
class name is com.tn.list.ListIter@ca0b6
the consumed memory is16
the consumed time is0
===================================
class name is com.tn.list.Loop@1a758cb
the consumed memory is272
the consumed time is16
===================================
当size=300000
class name is com.tn.list.Enume@757aef
the consumed memory is56
the consumed time is47
===================================
class name is com.tn.list.Iter@61de33
the consumed memory is12664
the consumed time is62
===================================
class name is com.tn.list.ListIter@ca0b6
the consumed memory is16
the consumed time is63
===================================
class name is com.tn.list.Loop@1a758cb
the consumed memory is272
the consumed time is47
===================================
当size =500000
class name is com.tn.list.Enume@757aef
the consumed memory is160
the consumed time is78
===================================
class name is com.tn.list.Iter@61de33
the consumed memory is16
the consumed time is110
===================================
class name is com.tn.list.ListIter@ca0b6
the consumed memory is272
the consumed time is93
===================================
class name is com.tn.list.Loop@1a758cb
the consumed memory is16
the consumed time is78
===================================
