Switch statement help please

Question

I have been advised on this forum that a switch statement in place of the if else etc would be neater. Could someone tell me where the switch statement goes in the code below.
Thanks
Calculator class Calculator.java
class Calculator {
public void Calculator() {
public double workOut(String s1) {
int count = 0, i_s1_len = 0, i_dot=0, i_neg =0;
double d_calc=0,d_num = 0, d_snum=0 ;
String s2 = "", s3 = "", s_num="";
if (s1.length()==0){ //Check for an input eg contains at least one character
System.out.println("Sorry you must input a equation ending in an equals '=' sign");
return 0;
else {
i_s1_len = s1.length();
count = 0; //reset count to zero
//remove spaces s2 becomes the equation
for (count=0; count+1 <= i_s1_len;){
if (s1.charAt(count)==32){
count++;
else{
s2=s2+s1.charAt(count);
count++;
i_s1_len = s2.length();//
// check final character is an "=" sign
if (s2.endsWith("=")){
else{
System .out.println( "Sorry your equation must end with an = sign ");
return 0;
// Checking if characters in the equation are legal eg 1-9 or ()-+/*. or the = sign is only at the end.
count = 0; //reset
for (count=0; count+1 <= i_s1_len;){
if ((s2.charAt(count)>39)&(s2.charAt(count)<58)){
count++;
else if ((s2.charAt(count)==61) & (count != i_s1_len-1)) {
System.out.println("Operator'=' is in two places ");
return 0;
else{
count++;
// Selecting Calculation type +-*/ and calculation Type and conversion
for (count=0; count+1 <= i_s1_len;){
//Addition calculation 43 = +
if (s2.charAt(count)== 43){
s3="+";
// Subtraction Calculation 45 = -
else if (s2.charAt(count)== 45){
s3="-";
// check for minus minus
if (s2.charAt(count+1)== 45){
s3="+";
// multiplication Calculation 42 = *
else if (s2.charAt(count)== 42){
s3="*";
// Division Calculation 47 =/
else if (s2.charAt(count)== 47){
s3="/";
//Get String for conversion to number
else s_num=s_num+s2.charAt(count);{
count++;
// Transfer number to single varable
while ((s2.charAt(count)>47)&(s2.charAt(count)<58)||(s2.charAt(count)==46)){
s_num=s_num+s2.charAt(count);
count++;
//check for multiple decimal points
if (s2.charAt(count-1)==46){
i_dot++;
if (i_dot > 1){
System.out.println("One of your numbers contains two decimals points ");
return 0;
i_dot=0; //reset decimal counter
// Get opperator + - * /
if (s3 =="+"){
d_num = d_num + Double.parseDouble(s_num);
else if (s3 =="-"){
d_num = d_num - Double.parseDouble(s_num);
else if (s3 =="*"){
d_num = d_num * Double.parseDouble(s_num);
else if (s3 =="/"){
if (Double.parseDouble(s_num)==0){
System.out.println("You are trying to divide by Zero which is infinity");
return 0;
d_num = d_num / Double.parseDouble(s_num);
else{
d_num = Double.parseDouble(s_num);
s_num="";
if (s2.length()==count+1) {
return d_num;
return d_num;

Answer 1

Instead of writing
if (x == 1)
    // do this
else if (x == 2)
    // do that
else
    // do the otheryou can write
switch (x) {
case 1:
    // do this
    break;
case 2:
    // do that
    break;
default:
    // do the other
    break;
}