Answered! I have problems for my add and substract methods. what I am returning in my add and substract method is null, but…

BigInt.java

import java.util.ArrayList;
class BigInt {
private ArrayList<Integer>list = new ArrayList<Integer>();
private ArrayList<Integer>answer = new ArrayList<Integer>();
private boolean pos=true;
private String number;
public Integer number1;
private String sign;
private Integer numberWithSign;
private String signAnswer;
BigInt(String num)
{
number = num;
numberWithSign = Integer.parseInt(num);

}

public boolean TestStringAndRemoveSign (){

if (number.length() >= 1) {
if (number.charAt(0) == ‘-‘){
pos = false;
number = number.substring(1);
if (number.length() == 0){
return false;
}
else {
return true;
}
}
if (number.charAt(0) == ‘+’){
number = number.substring(1);
pos = true;
if (number.length() == 0){
return false;
}
else {
return true;
}
}
if (number.length() == 0){
return false;}
else {
return true;
}
}
else {
return false;
}
}
public void Store(){
if(TestStringAndRemoveSign()){
for (int i = (number.length() – 1); i >= 0 ; i–){
if (Character.isDigit(number.charAt(i))){
number1 = Character.getNumericValue(number.charAt(i));
list.add(number1);
}
else{
System.out.println( “throw new BigIntOutOfBoundsException Wrong format”);
}
}
}
else{
System.out.println(“throw new BigIntOutOfBoundsException Wrong format”);
}
}
public String ToString(){
String display = “”;
if (pos == true){
sign = “”;
}
if (pos == false){
sign = “-“;
}
display = display + sign;
for (int i = number.length()-1; i>=0; i–){
display = display + list.get(i);
}

return display;

}
public void FixLength(BigInt other){
if (list.size()>other.list.size()){
for (int b=other.list.size(); b<list.size();b++){
other.list.add(0);
}
}
if (list.size()<other.list.size()){
for (int b=list.size(); b<other.list.size();b++){
other.list.add(0);
}
}
}
public BigInt add(BigInt other){

FixLength(other);

if (pos ==other.pos){
for (int a =0; a<=list.size() – 1; a++){
answer.add(list.get(a) + other.list.get(a));
}
for(int k=0; k<=answer.size() – 1; k++){
if(answer.get(k)>= 10){
answer.set(k,answer.get(k)-10);
answer.set(k+1,answer.get(k+1)+1);
}
}
Integer finalAnswer;
finalAnswer = numberWithSign + other.numberWithSign;
if (finalAnswer.toString().charAt(0) == ‘-‘){
signAnswer = “-“;
}
else{
signAnswer = “”;
}
String display = “”;
display = display + signAnswer ;
for(int c=answer.size()-1; c>=0; c–){
display = display + answer.get(c);
}
//addition result is stored in display.

BigInt sum= new BigInt(String.valueOf(display)); //new BigInt is created for added value
System.out.println(“addition : ” +sum.numberWithSign); //display the added results
return sum;

}
//if sign is different for both integers. then call the substraction methods.
else{
BigInt s=new BigInt(String.valueOf(numberWithSign));
s.Store();
BigInt b =s.substract(other);
}
return null;
}
public BigInt substract(BigInt other){
FixLength(other);
Integer sub;
Integer IntNumber;
Integer otherIntNumber;
IntNumber = Integer.parseInt(number);
otherIntNumber = Integer.parseInt(other.number);
if (IntNumber > otherIntNumber || IntNumber==otherIntNumber){
for (int a =0; a<=list.size() – 1; a++){
if (list.get(a)<other.list.get(a)){
list.set(a,list.get(a)+10);
list.set(a+1,list.get(a+1)-1);
}
answer.add(list.get(a) – other.list.get(a));
}
}
else{
for (int a =0; a<=list.size() – 1; a++){
if(list.get(a)>other.list.get(a)){
other.list.set(a,other.list.get(a)+10);
other.list.set(a+1,other.list.get(a+1)-1);
}
answer.add(other.list.get(a)-list.get(a));
}
}
Integer finalAnswer;
finalAnswer = numberWithSign – other.numberWithSign;
if (finalAnswer.toString().charAt(0) == ‘-‘){
signAnswer = “-“;
}
else{
signAnswer = “”;
}
String display = “”;
display = display + signAnswer ;
for(int c=answer.size()-1; c>=0; c–){
display = display + answer.get(c);
}
//substracted results is stored in subvalue
BigInt subvalue= new BigInt(String.valueOf(display));
System.out.println(“substraction : ” +subvalue.numberWithSign); //results is displayed
return subvalue;

}
}

//my java class that test the program

//package bigint;

public class BigIntDemo {
public static void main(String[] args) {

BigInt b1 = new BigInt(“-652234”);
//System.out.println(b1);
BigInt b2 = new BigInt(“4567”);
BigInt b3;
b1.Store();
b2.Store();

System.out.println(“b1 is ” + b1.ToString());
System.out.println(“b2 is ” + b2.ToString());
b3 = b1.add(b2);
;

}
}

output1:

output2:

//try with your testcases.. it works fine…for any clarification or modification tell me in comment section.. dont forget to upvote..