1.String a = "abc";
String b ="def";
String c = a+b;
2.StringBuffer a =new StringBuffer("acb");
StringBuffer b =new StringBuffer("123");
a.append(b);
3.String a = "abc";
String b ="def";
String c = a.concat(b);
第三种方法,必须是String 类型
string a="a";
string b="b";
string c=a+b;