public class Test {
    
    // 0-9的ASCII码:48-57
    // a-z的ASCII码:97-122
    // A-Z的ASCII码：65-90 
    public static void main(String[] args) {
        String str = "asdJKL234+-*";
        char[] ch  = str.toCharArray();
        for (int i = 0; i < ch.length; i++) {
            if(ch[i]>=65 && ch[i]<=90){
                ch[i]=(char)(ch[i]+32);
            }else if(ch[i]>=97 && ch[i]<=122){
                ch[i]=(char)(ch[i]-32);
            }else if(ch[i]<48 || ch[i]>57){
                ch[i] = '*';
            }
        }
        String newStr = new String(ch);
        System.out.println(newStr);
    }
}

------解决方案--------------------
for example
Java code
String s = "asdJKL234+-*";
StringBuilder buf = new StringBuilder();
for (char c : s.toCharArray()) {
    if (c>='a' && c<='z') {
        buf.append((char)(c+('A'-'a')));
    } else if (c>='A' && c<='Z') {
        buf.append((char)(c+('a'-'A')));
    } else if (c>='0' && c<='9'){
        buf.append(c);
    } else {
        buf.append("*");
    }
}
String result = buf.toString();
System.out.println(result);

------解决方案--------------------
String s = "asdJKL234+-*";
StringBuilder buf = new StringBuilder();
for (char c : s.toCharArray()) {
   if (c>='a' && c<='z') {
       buf.append((char)(c+('A'-'a')));
   } else if (c>='A' && c<='Z') {
       buf.append((char)(c+('a'-'A')));
   } else if (c>='0' && c<='9'){
       buf.append(c);
   } else {
       buf.append("*");
   }
}
String result = buf.toString();
System.out.println(result);


------解决方案--------------------
Java code

    public String format(String str ){
        StringBuffer sb = new StringBuffer();
        char c[] = str.toCharArray();        //得到字符串的字节数组
        for(char temp : c){
            String s = new Character(temp).toString();    //取出一个字符转换成String类型
            if(s.matches("\\p{Lower}")){    //如果该字符是小写的就转换成大写的
                s = s.toUpperCase();
            }else if(s.matches("\\p{Upper}")){     //如果该字符是是大写的，就转换成小写的
                s = s.toLowerCase();
            }else if(s.matches("\\d")){
                //不用做什么
            }else{        //将非数字和字母的字符变成*
                s = "*";
            }
            sb.append(s);
        }    
        return sb.toString();
    }