//用内存,将小写字母替换成大写字母 String str = "helloworld,goodmorning"; ByteArrayOutputStream bos = null; ByteArrayInputStream bis = null; bis = new ByteArrayInputStream(str.getBytes()); bos = new ByteArrayOutputStream(); int temp = -1; while( (temp = bis.read()) != -1 ) //依次读取内存 { //接收字符 char c = (char) temp; bos.write(Character.toUpperCase(c)); //输出 } //取出内存中的内容 String newStr = bos.toString(); System.out.println(newStr);