Run time error in java! why?

import java.io.BufferedReader;
import java.io.PrintWriter;
import java.io.InputStreamReader;

class DhapuandHammingDistance {
public static void main(String arg[])throws Exception{
	BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
	PrintWriter pr=new PrintWriter(System.out,true);

int t,c,i,l1,l2;
char c1[],c2[];
t=Integer.parseInt(br.readLine());
while(t-->0){
	c1=br.readLine().toCharArray();
	c2=br.readLine().toCharArray();
	l1=c1.length;l2=c2.length;c=0;
	if(l1!=l2)
		pr.println(-1);
	else{
		for(i=0;i<l1;i++){
			if(c1[i]!=c2[i])
				c++;
		}

	pr.println(c);
	}}}}

You are converting string to character array simultaneously when you are taking input this is leading to runtime error.
Read [here][1] for how to convert string to character array in java.

Correction:

  1. take string as input first,

  2. then convert it to character array

[Here][2] is your corrected code.

P.S. - You still need to check ur logic for the problem.
[1]: Converting String to "Character" array in Java - Stack Overflow
[2]: tm0TUo - Online Java Compiler & Debugging Tool - Ideone.com

i am getting runtime error on codechef not on my eclipse

also getting runtime error in this there is no string

import java.io.BufferedReader;
import java.io.PrintWriter;
import java.io.InputStreamReader;
import java.util.Arrays;
class ComplementaryCouples {
public static void main(String arg[])throws Exception{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
PrintWriter pr=new PrintWriter(System.out,true);

int n,i,j,l,h,m,c=0;
long k,a[],num;
n=Integer.parseInt(br.readLine());
k=Long.parseLong(br.readLine());
a=new long[n];
for(i=0;i<n;i++)
	a[i]=Integer.parseInt(br.readLine());

Arrays.sort(a);
for(j=0;j<n;j++){
num=k-a[j];	
l=j+1;h=a.length-1;	

while(l<=h){
	m=(l+h)/2;
	if(a[m]==num){
		c=1;break;
	}
	else if(a[m]<num)
		l=m+1;
	else
		h=m-1;
}


}
if(c==1)
	pr.println("YES");
else
	pr.println("NO");
}}

Please give more information about the problem which you are attempting. Format your code correctly or give link, it is too clumsy to read.

Read how to ask a question here.

Which problem you are attempting to solve ??