int one = 10 ;
int two = 20 ;
int three = 0 ;
three=one+two;
System.out.println("three = one + two ==>"+three);
这里中间的three的前面为什么不用加变量类型？
因为第三行定义过了three（ int three = 0 ;）定义了的变量后面直接引用就是了