要输出three+=one==>40,但为啥（）里面还要+three呢
int one=10;
int two=20;
three=one+two
System.out.println("three=one+two==>"+three);
three+=one;
System.out.println("three+=one==>"+three)System.out.println（这里面的+好是起到连接作用，将后面那个three值转化为String类和前面的three=one+two==>连接起来。）这样你输出的才会是three=one+two==>（three的值）