public class StringAPIDemo09{  
    public static void main(String args[]){  
        System.out.println("将\"hello world\"转成大写：" + "hello world".toUpperCase()) ;  
        System.out.println("将\"HELLO WORLD\"转成小写：" + "HELLO WORLD".toLowerCase()) ;  
    }  
};  

//源代码片段来自云代码http://yuncode.net