|
|
|
[blockquote]/*300*250，创建于2011-2-24*/ var cpro_id = 'u388789';
-
[/blockquote]
1. 概述
在java中，参数传递是通过传值（对于对象类型，传递的是引用的拷贝），所以常规的交换实现不了两个对象的交换，下面是测试代码：
Java代码
import org.apache.commons.beanutils.BeanUtils;
public class Employee {
// Properties
private int id;
private String name;
// Constructors
public Employee() {
}
public Employee(int id, String name) {
this.id = id;
this.name = name;
}
// get、set methods
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
// 无效的交换
public static void swap(Employee x, Employee y) {
Employee temp = x;
x = y;
y = temp;
}
// 使用 BeanUtils 方法的有效交换
public static void swapByBeanUtils(Employee x, Employee y) {
try {
// clone x to temp
Employee temp = (Employee)BeanUtils.cloneBean(x);
// copyProperties from y to x
BeanUtils.copyProperties(x, y);
// copyProperties from temp to y
BeanUtils.copyProperties(y, temp);
// then, the Properties values of x,y has been swaped.
} catch (Exception e) {
e.printStackTrace();
}
}
// 有人提出使用交换数组等集合里的元素 来实现交换，这样也是无效的
public static void swapByArray(Object[] a, int i, int j) {
Object t = a;
a = a[j];
a[j] = t;
}
public static void main(String[] args) {
Employee a = new Employee(1, "Bob");
Employee b = new Employee(2, "Jack");
// 直接方法调用交换 -- NO
// swap(a, b);
// 利用BeanUtils交换 -- YES
// swapByBeanUtils(a, b);
// 利用 交换数据 思想 -- NO
// Object[] o = {a, b};
// swapByArray(o, 0, 1);
// 直接交换 -- YES
// Employee temp = a;
// a = b;
// b = temp;
System.out.println(a);
System.out.println(b);
}
// method for print
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("id: ").append(id).append(" name: ").append(name);
return sb.toString();
}
}
import org.apache.commons.beanutils.BeanUtils;
public class Employee {
// Properties
private int id;
private String name;
// Constructors
public Employee() {
}
public Employee(int id, String name) {
this.id = id;
this.name = name;
}
// get、set methods
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
// 无效的交换
public static void swap(Employee x, Employee y) {
Employee temp = x;
x = y;
y = temp;
}
// 使用 BeanUtils 方法的有效交换
public static void swapByBeanUtils(Employee x, Employee y) {
try {
// clone x to temp
Employee temp = (Employee)BeanUtils.cloneBean(x);
// copyProperties from y to x
BeanUtils.copyProperties(x, y);
// copyProperties from temp to y
BeanUtils.copyProperties(y, temp);
// then, the Properties values of x,y has been swaped.
} catch (Exception e) {
e.printStackTrace();
}
}
// 有人提出使用交换数组等集合里的元素 来实现交换，这样也是无效的
public static void swapByArray(Object[] a, int i, int j) {
Object t = a;
a = a[j];
a[j] = t;
}
public static void main(String[] args) {
Employee a = new Employee(1, "Bob");
Employee b = new Employee(2, "Jack");
// 直接方法调用交换 -- NO
// swap(a, b);
// 利用BeanUtils交换 -- YES
// swapByBeanUtils(a, b);
// 利用 交换数据 思想 -- NO
// Object[] o = {a, b};
// swapByArray(o, 0, 1);
// 直接交换 -- YES
// Employee temp = a;
// a = b;
// b = temp;
System.out.println(a);
System.out.println(b);
}
// method for print
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("id: ").append(id).append(" name: ").append(name);
return sb.toString();
}
}
2. 结论
在java中，对象引用是通过值来传递的，方法不能修改参数指向新的对象。
注：需加载 BeanUtils包
|
|
|
发表于 2011-9-12 22:06:32