Change letter case from of all character in any string in java

//To display the string after the case of each characters
import java.io.*;
public class change_case
{
public static void main()throws IOException
{
InputStreamReader isr=new InputStreamReader(System.in);
BufferedReader br=new BufferedReader(isr);
char ch,chr=0;
String s1,s2=" ";
int i,j,c=0;
System.out.println("Enter string 1");
s1=br.readLine();
i=s1.length();
for(j=0;j<i;j++)
{
ch=s1.charAt(j);
if(ch>='A'&&ch<='Z')
{
chr=Character.toLowerCase(ch);
s2=s2+chr;
}
if(ch>='a'&&ch<='z')
{
chr=Character.toUpperCase(ch);
s2=s2+chr;
}
if(ch==' ')
s2=s2+" ";
}
System.out.print(s2);
}
}