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锁定老帖子 主题：两段java代码的比较
精华帖 (0) :: 良好帖 (16) :: 新手帖 (0) :: 隐藏帖 (0)
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| 作者 | 正文 |
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发表时间：2008-06-02
Eastsun 写道 Java doesn't support this optimization for a number of reasons, including：
* the security model requires stack frame information * reflection relies on "stack crawling" * stack traces would be incomplete * debugging would be problematic You have the points. BTW: It seems FF3 RC1 is not well supported by JavaEye. |
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发表时间：2008-06-02
俺这个递归运行良好，如果从root object开始执行（一个XML的root element），大约100多个对象实例
package byd.biz;
import javax.ejb.Stateless;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
/**
*
* @author ll258583
*/
@Stateless(name = "xoServiceBean")
public class xoServiceBean implements xoServiceLocal {
@PersistenceContext(unitName = "xoServicePU")
private EntityManager em;
/**
* Set JAXB object's value to the EntityBean object
* @param jxo
* @param eto
*/
@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public void x2o(Object jxo, Object eto) {
System.out.println("------------------------------------------------------------------");
System.out.println(eto.getClass().getName());
//validate if two papramater are matchable
if (eto.getClass().getPackage().getName().equals("byd.entity") && jxo.getClass().getPackage().getName().equals("byd.xoMapping.pip4A3") && eto.getClass().getName().substring(12).equals(jxo.getClass().getName().substring(21))) {
Field[] etoDeclaredFields = eto.getClass().getDeclaredFields();
Field[] jxoDeclaredFields = jxo.getClass().getDeclaredFields();
for (int i = 0; i < etoDeclaredFields.length; i++) {
for (int j = 0; j < jxoDeclaredFields.length; j++) {
Field etoField = etoDeclaredFields[i];
Class etoFieldType = etoField.getType();
String etoFieldName = etoField.getName();
Field jxoField = jxoDeclaredFields[j];
String jxoFieldName = jxoField.getName();
try {
if (etoFieldName.toLowerCase().equals(jxoFieldName.toLowerCase())) {
if (etoFieldType.getName().equals("java.lang.String")) {
//in case of basic type(java.lang.String) filed
System.out.println(etoFieldName + " : " + etoFieldType.getName());
Class<?>[] paras = null;
Object[] args = null;
Method jxoGetMethod = jxo.getClass().getDeclaredMethod("get" + jxoFieldName.substring(0, 1).toUpperCase() + jxoFieldName.substring(1), paras);
String value = (String) jxoGetMethod.invoke(jxo, args);
if (value != null) {
Method etoSetMethod = eto.getClass().getDeclaredMethod("set" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), etoFieldType);
etoSetMethod.invoke(eto, value);
} else {
System.out.println("STRING IS NULL");
}
} else if (etoFieldType.getName().equals("java.util.List")) {
//in case of java.util.List field
System.out.println(etoFieldName + " : " + etoFieldType.getName());
Class<?>[] paras = null;
Object[] args = null;
Method jxoGetMethod = jxo.getClass().getDeclaredMethod("get" + jxoFieldName.substring(0, 1).toUpperCase() + jxoFieldName.substring(1), paras);
Method etoGetMethod = eto.getClass().getDeclaredMethod("get" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), paras);
List jxoMemberList = (List) jxoGetMethod.invoke(jxo, args);
if (jxoMemberList.size() != 0 && jxoMemberList != null) {
List etoMemberList = (List) etoGetMethod.invoke(eto, args);
etoMemberList = new ArrayList();
for (Object jxm : jxoMemberList) {
Class C = Class.forName("byd.entity._" + jxm.getClass().getName().substring(21));
Object etm = C.newInstance();
this.x2o(jxm, etm);
etoMemberList.add(etm);
}
} else {
System.out.println("LIST IS EMPTY OR NULL");
}
} else if (etoFieldType.getName().equals("java.util.ArrayList")) {
//in case of java.util.ArrayList<String>() field
System.out.println(etoFieldName + " : " + etoFieldType.getName());
Class<?>[] paras = null;
Object[] args = null;
Method jxoGetList = jxo.getClass().getDeclaredMethod("get" + jxoFieldName.substring(0, 1).toUpperCase() + jxoFieldName.substring(1), paras);
List<String> stringList_1 = (List<String>) jxoGetList.invoke(jxo, args);
if (stringList_1 != null && stringList_1.size() != 0) {
Method etoGetList = eto.getClass().getDeclaredMethod("get" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), paras);
ArrayList stringList_2 = (ArrayList) etoGetList.invoke(eto, args);
stringList_2 = new ArrayList<String>();
for (String str_1 : stringList_1) {
String str_2 = new String(str_1);
stringList_2.add(str_2);
}
} else {
System.out.println("ArrayList<String> IS NULL OR EMPTY");
}
} else {
//in case of other class type field
System.out.println(etoFieldName + " : " + etoFieldType.getName());
Class<?>[] paras = null;
Object[] args = null;
Method jxoGetMethod = jxo.getClass().getDeclaredMethod("get" + jxoFieldName.substring(0, 1).toUpperCase() + jxoFieldName.substring(1), paras);
Object nextJxo = jxoGetMethod.invoke(jxo, args);
if (nextJxo != null) {
// Method etoGetMethod = eto.getClass().getDeclaredMethod("get" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), paras);
Method etoSetMethod = eto.getClass().getDeclaredMethod("set" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), etoFieldType);
Object nextEto = etoFieldType.newInstance();
etoSetMethod.invoke(eto, nextEto);
this.x2o(nextJxo, nextEto);
} else {
System.out.println(jxoFieldName + " IS NULL");
}
}
}
} catch (ClassNotFoundException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (IllegalArgumentException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (InvocationTargetException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (NoSuchMethodException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (SecurityException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
} else {
// throw new UnmatchableException();
System.out.println("UnmatchableException");
}
//persist the entityBean object's value
System.out.println("Persist : " + eto.getClass().getName());
em.persist(eto);
}
/**
* Set EntityBean's value to the JAXB object
* @param eto
* @param jxo
*/
@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public void o2x(Object eto, Object jxo) {
System.out.println("------------------------------------------------------------------");
System.out.println(eto.getClass().getName());
//validate if two papramater are matchable
if (eto.getClass().getPackage().getName().equals("byd.entity") && jxo.getClass().getPackage().getName().equals("byd.xoMapping.pip4A3") && eto.getClass().getName().substring(12).equals(jxo.getClass().getName().substring(21))) {
Field[] etoDeclaredFields = eto.getClass().getDeclaredFields();
Field[] jxoDeclaredFields = jxo.getClass().getDeclaredFields();
for (int i = 0; i < jxoDeclaredFields.length; i++) {
for (int j = 0; j < etoDeclaredFields.length; j++) {
Field jxoField = jxoDeclaredFields[i];
String jxoFieldName = jxoField.getName();
Field etoField = jxoDeclaredFields[j];
String etoFieldName = etoField.getName();
try {
if (etoFieldName.toLowerCase().equals(jxoFieldName.toLowerCase())) {
if (jxoField.getType().getName().equals("java.lang.String")) {
//in case of basic type(java.lang.String) filed
System.out.println(jxoField.getName() + " : " + jxoField.getType().getName());
Class<?>[] paras = null;
Object[] args = null;
Method etoGet = eto.getClass().getDeclaredMethod("get" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), paras);
String value = (String) etoGet.invoke(eto, args);
if (value != null) {
Method jxoSet = jxo.getClass().getDeclaredMethod("set" + jxoFieldName.substring(0, 1).toUpperCase() + jxoFieldName.substring(1), jxoField.getType());
jxoSet.invoke(jxo, value);
} else {
System.out.println("STRING IS NULL");
}
} else if (jxoField.getType().getName().equals("java.util.List")) {
//in case of collection(java.util.List) field
System.out.println(jxoField.getName() + " : " + jxoField.getType().getName());
Class<?>[] paras = null;
Object[] args = null;
Method etoGetList = eto.getClass().getDeclaredMethod("get" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), paras);
List etoList = (List) etoGetList.invoke(eto, args);
if (etoList.size() != 0 && etoList != null) {
Method jxoGetList = jxo.getClass().getDeclaredMethod("get" + jxoFieldName.substring(0, 1).toUpperCase() + jxoFieldName.substring(1), paras);
List jxoList = (List) jxoGetList.invoke(jxo, args);
jxoList = new ArrayList();
for (Object etm : etoList) {
Class C = Class.forName("byd.xoMapping.pip4A3." + etm.getClass().getName().substring(12));
Object jxm = C.newInstance();
this.o2x(etm, jxm);
jxoList.add(jxm);
}
} else {
System.out.println("LIST IS NULL OR EMPTY");
}
} else if (etoField.getType().getName().equals("java.util.ArrayList")) {
//in case of ArrayList<String> field
System.out.println(jxoField.getName() + " : " + jxoField.getType().getName());
Class<?>[] paras = null;
Object[] args = null;
Method etoGetList = eto.getClass().getDeclaredMethod("get" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), paras);
ArrayList<String> stringList_1 = (ArrayList<String>) etoGetList.invoke(jxo, args);
if (stringList_1 != null && stringList_1.size() != 0) {
Method jxoGetList = jxo.getClass().getDeclaredMethod("get" + jxoFieldName.substring(0, 1).toUpperCase() + jxoFieldName.substring(1), paras);
List stringList_2 = (List) jxoGetList.invoke(jxo, args);
stringList_2 = new ArrayList<String>();
for (String str_1 : stringList_1) {
String str_2 = new String(str_1);
stringList_2.add(str_2);
}
} else {
System.out.println("ArrayList<String> IS NULL OR EMPTY");
}
} else {
//in case of other class type field
Class<?>[] paras = null;
Object[] args = null;
Object arg = null;
Method etoGet = eto.getClass().getDeclaredMethod("get" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), paras);
Object nextEto = etoGet.invoke(jxo, arg);
if (nextEto != null) {
Method jxoSet = jxo.getClass().getDeclaredMethod("set" + etoFieldName.substring(0, 1).toUpperCase() + etoFieldName.substring(1), jxoField.getType());
Object nextJxo = jxoField.getType().newInstance();
jxoSet.invoke(jxo, nextJxo);
this.o2x(nextEto, nextJxo);
} else {
System.out.println(etoFieldName + " IS NULL");
}
}
}
} catch (InstantiationException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (ClassNotFoundException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (IllegalArgumentException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (InvocationTargetException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (NoSuchMethodException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
} catch (SecurityException ex) {
Logger.getLogger(xoServiceBean.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
} else {
// throw new UnmatchableException();
System.out.println("UnmatchableException");
}
}
}
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发表时间：2008-06-02
楼上代码看不懂~！
你方法里的代码是不是太长了啊~！ 呵呵 |
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发表时间：2008-06-03
楼上的楼上的代码好长
我以前写的递归基本上没有创建大的对象，所以没有碰到此问题，今天楼主提出来了，以后恐怕得多注意了 |
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发表时间：2008-06-03
以前遇到过这种问题, 最后还是改成循环调用解决的 ,
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发表时间：2008-06-05
递归 出栈入栈的事肯定多
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发表时间：2008-06-05
一般来说没有大问题的。除非很大的递归。这个一般也可以当作性能问题考虑，不用太早考虑，更用不着把一切递归的方法都改成循环。
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发表时间：2008-06-05
Lucas Lee 写道 一般来说没有大问题的。除非很大的递归。这个一般也可以当作性能问题考虑，不用太早考虑，更用不着把一切递归的方法都改成循环。
嗯，这仅仅是对OOM问题的分析做多一种设想。 |
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发表时间：2008-06-05
import java.util.ArrayList;
import java.util.List;
public class TailRecursionTest {
public static void main(String[] args) {
TailRecursionTest t = new TailRecursionTest();
t.a(0);
}
public void a(int j) {
System.out.println(j);
j++;
if (j<10000) //if (j!=10000) 也可以
return;
List list = new ArrayList<Integer>(100000);
a(j);
}
}
递归 ，学习，以上我把if条件小改动了下，可以成功，不知道怎么解释：） |
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发表时间：2008-06-05
leelj 写道
import java.util.ArrayList;
import java.util.List;
public class TailRecursionTest {
public static void main(String[] args) {
TailRecursionTest t = new TailRecursionTest();
t.a(0);
}
public void a(int j) {
System.out.println(j);
j++;
if (j<10000) //if (j!=10000) 也可以
return;
List list = new ArrayList<Integer>(100000);
a(j);
}
}
递归 ，学习，以上我把if条件小改动了下，可以成功，不知道怎么解释：） 无语了，0<10000，一次还没跑完。 |
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