Can some help me write this program?

Write an interactive Java program to Output an signed decimal number between -128 and 127 corresponding to an input 8-bit binary number(a string)in the twos complement system, and

Output an 8-bit binary number (as a string)in the twos complement system corresponding to an input signed decimal number between -128 and 127.

Ive already written a java program (see below) that would convery from bintodec and vice vera, but I need to modify the two methods so that they work for signed integers instead of unsigned integers

import java.util.Scanner;

public class lab2 {

public static void main(String[] args) {

int choice, decimal;

String binary;

Scanner sc = new Scanner(System.in);

while (true) {

System.out.println("~~~Select any one from below~~~ " // displays menu

+ "1. Convert decimal to binary " + "2. Convert binary to decimal " + "3. Quit ");

choice = sc.nextInt(); // stores the users input as a choice

if (choice == 1) {

System.out.println(" Enter decimal: ");

decimal = sc.nextInt();

binary = decToBin(decimal); // calls dectobin

System.out.println(" " + decimal + " in binary is " + binary + " ");

} else if (choice == 2) {

System.out.println("Enter binary: ");

sc.nextLine();

binary = sc.nextLine();

decimal = binToDec(binary); // calls bintodec

System.out.println(" " + binary + " in decimal is " + decimal + " ");

} else {

System.out.println(" Program terminated"); // program ends

break;

}

}

}

public static String decToBin(int x) {

String bin = ""; // store the bin string

int rem;

for (int i = 0; i < 8; i++) { // runs until you get the 8 bit

rem = x % 2; // rem is remainer of the dec / 2

x = x / 2; // x is the dec divided by 2

bin = rem + bin; // the binary number is the remainder and its stored in bin

}

return bin;

}

public static int binToDec(String s) {

int num = 0;

for (int i = 7; i >= 0; i--) // i is the power

if (s.charAt(i) == '1') // if 1 appears, it takes 2^(7-i)

num = num + (int) Math.pow(2, 7 - i);

return num;

}

}