//判断输入的字符是否是字母
import java.io.*;
public class HelloWorldClass
{
public static void main(String[] args)
{
new HelloWorldClass().output();
}
public HelloWorldClass(){ }
public void output()
{
Input myinput=new Input();
char c=myinput.getThechar();
if(c>=65&c<=90||c>=97&c<=122)
System.out.println("It is a letter. The letter is :"+c);
else
System.out.println("It is not a letter :");
}
class Input
{ public char getTheChar()
{
char c=0;
System.out.println("Enter a character :");
try{
c=(char) System.out.read();
}catch(IOException(e){};

错的很多，我这样写的

import java.io.*;

public class Test {
public static void main(String[] args) throws Exception{
System.out.println("请输入字符");
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String letter = in.readLine();
if(Character.isLetter(letter.toCharArray()[0])) {
System.out.println("是字母");
} else {
System.out.println("不是字母");
}
}
}

楼主的错误太多了,建议把一些基本的IO看一下,楼上的差不多