SIGTSTP error in java

please check my code. getting sigtstp error

import java.util.;
import java.lang.
;
import java.io.*;

/* Name of the class has to be “Main” only if the class is public. */
class Codechef
{
public static void main (String[] args) throws java.lang.Exception
{
// your code goes here
int T, total;
Scanner sc = new Scanner(System.in);
total = sc.nextInt();
T = 1;
while(T<=total)
{
String St1 ;
String St2 ;
String St = “”;
char[] st;
St1 = sc.nextLine();
St2 = sc.nextLine();
int z1=St1.length();
int z2=St2.length();
int a[] = new int[27];
Arrays.fill(a, 0);
char[] st1 = St1.toCharArray();
char[] st2 = St2.toCharArray();
for(int i=0; i<z1; i++)
{
a[st1[i]-‘a’]++;
}
for(int j=0; j<z2; j++)
{
a[st2[j]-‘a’]–;
}
int a2[] = new int[27];
Arrays.fill(a2, 0);
for (int i = 0; i < 27; i++) {
a2[i] = a[i];
}

	for(int i=0; i<=(st2[0]-'a'); i++)
	{   
		while(a[i]!=0)
		{
			St+=((char)(i+97));
			a[i]--;
		}
	}
	St = St + St2;
	for(int j=0; j<26; j++)
	{
		while(a[j]!=0)
		{
			St+=((char)(j+97));
			a[j]--;
		}
	}
	String Stt = "";
	for(int i=0; i<=(st2[0]-'a'); i++)
	{   
		while(a[i]>0)
		{
			Stt+=((char)(i+97));
			a[i]--;
		}
	}
	Stt = Stt + St2;
	for(int j=0; j<26; j++)
	{
		while(a[j]>0)
		{
			Stt+=((char)(j+97));
			a[j]--;
		}
	}
	System.out.println(St);
	T = T + 1;
}

    
}

}

what’s the problem you’re trying to solve?