面试题：实现两个整数变量的交换

================方法一==================

class LianXi{
 public static void main(String [] args){
  int a = 10;
  int b =20;
  System.out.println("a="+a+",b="+b);
  int c =a;
  a = b;
  b = c;
  System.out.println("a="+a+",b="+b);
 }
}
结果：
a=10,b=20
a=20,b=10
======================方法二=====================
class LianXi{
 public static void main(String [] args){
  int a = 10;
  int b =20;
  System.out.println("a="+a+",b="+b);
  a =a^b;  
  b =a^b;   //(a^b) ^b = a
  a =a^b;  //(a^b)^a =b
  System.out.println("a="+a+",b="+b);

 }
}
结果：
a=10,b=20
a=20,b=10

===============方法三================
class LianXi{
 public static void main(String [] args){
  int a = 10;
  int b =20;
  System.out.println("a="+a+",b="+b);
  a =a+b;     //a =10+20=30
  b =a-b;     //b=30-20 =10
  a =a-b;    //a=30-10=20
  System.out.println("a="+a+",b="+b);

 }
}
结果：
a=10,b=20
a=20,b=10
===============方法四=================
class LianXi{
 public static void main(String [] args){
  int a = 10;
  int b =20;
  System.out.println("a="+a+",b="+b);
  b =(a+b)-(a=b);     //b = (10+20) -(20) =10       a=20
  System.out.println("a="+a+",b="+b);

 }
}  
结果：
a=10,b=20
a=20,b=10