//Tested on Eclipse and both class should be in same package import java.util.Scanner; public class P3 { /*isInteger method implementation * @param String type * while parsing if it throw exception then it is not integer * else it is integer*/ public static Boolean isDouble(String token){ try { Double.parseDouble(token); } catch(NumberFormatException e) { System.out.println(\"Invalid Operand\"); return false; } catch(NullPointerException e) { System.out.println(\"Invalid Operand\"); return false; } // only got here if we didn\'t return false return true; } public static String evaluate(String expression) { // Print expression System.out.print(expression); // Declare variables for operands, operator, result, and return value double operand1=0,operand2 = 0,result=0; char operator; Boolean flag=Boolean.FALSE;//for if operators were not listed String returnString = \"\"; String token[]=new String[expression.length()];//for storing all token from expression // Create Scanner object to parse expression // create a new scanner with the specified String Object int i=0; Scanner scanner = new Scanner(expression); while(scanner.hasNext()){ token[i]=scanner.next(); i++; } scanner.close(); // Compute a numerical result for the expression if(isDouble(token[0])){ operand1=Double.parseDouble(token[0]); } if(isDouble(token[2])){ operand2=Double.parseDouble(token[2]); } operator=token[1].charAt(0); if(operand1!=0&&operand2!=0){ switch(operator){ case \'+\': result=operand1+operand2; break; case \'-\': result=operand1-operand2; break; case \'*\': result=operand1*operand2; break; case \'/\': result=operand1/operand2; break; case \'%\': result=operand1%operand2; break; case \'^\': result=Math.pow(operand1, operand2); break; default: System.out.println(\"Invalid Operator\"); flag=Boolean.TRUE; break; } // Convert numerical result to string returnString=Double.toString(result); if(flag){ return null; } // Return result return returnString; }else{ return null; } } } /*********Calculator class***************/ import java.util.Scanner; /*Calculator class start*/ public class Calculator { public static void main(String args[]){ /*Variable declaration*/ String expression; /*Scanner object for input*/ Scanner input=new Scanner(System.in); /*Prompt for expression*/ System.out.println(\"Please Enter expression\"); expression=input.nextLine(); input.close(); /*Calling Evaluate method*/ String result=P3.evaluate(expression); /*Printing result if it is not null*/ if(result!=null) { System.out.println(result); } } } /***************output************/ Please Enter expression 11.22 + 3.456 = 11.22 + 3.456 =14.676 Please Enter expression 5.555 - 32.14 = 5.555 - 32.14 =-26.585 Please Enter expression 25634.8 * .32 = 25634.8 * .32 = 8203.136 Please Enter expression 5 ^ 4 = 5 ^ 4 =625.0 Please Enter expression Whatever + 2 = Whatever + 2 =Invalid Operand Please Enter expression 4.0 - 1.2.3 = 4.0 - 1.2.3 =Invalid Operand Please Enter expression 1.234 $ 0.5 = 1.234 $ 0.5 =Invalid Ope.

1. //Tested on Eclipse and both class should be in same package
import java.util.Scanner;
public class P3 {
/*isInteger method implementation
* @param String type
* while parsing if it throw exception then it is not integer
* else it is integer*/
public static Boolean isDouble(String token){
try {
Double.parseDouble(token);
} catch(NumberFormatException e) {
System.out.println("Invalid Operand");
return false;
} catch(NullPointerException e) {
System.out.println("Invalid Operand");
return false;
}
// only got here if we didn't return false
return true;
}
public static String evaluate(String expression) {
// Print expression
System.out.print(expression);
// Declare variables for operands, operator, result, and return value
double operand1=0,operand2 = 0,result=0;
char operator;
Boolean flag=Boolean.FALSE;//for if operators were not listed
String returnString = "";
String token[]=new String[expression.length()];//for storing all token from expression
// Create Scanner object to parse expression
// create a new scanner with the specified String Object
int i=0;
Scanner scanner = new Scanner(expression);
while(scanner.hasNext()){
token[i]=scanner.next();

2. i++;
}
scanner.close();
// Compute a numerical result for the expression
if(isDouble(token[0])){
operand1=Double.parseDouble(token[0]);
}
if(isDouble(token[2])){
operand2=Double.parseDouble(token[2]);
}
operator=token[1].charAt(0);
if(operand1!=0&&operand2!=0){
switch(operator){
case '+':
result=operand1+operand2;
break;
case '-':
result=operand1-operand2;
break;
case '*':
result=operand1*operand2;
break;
case '/':
result=operand1/operand2;
break;
case '%':
result=operand1%operand2;
break;
case '^':
result=Math.pow(operand1, operand2);
break;
default:
System.out.println("Invalid Operator");
flag=Boolean.TRUE;
break;
}

3. // Convert numerical result to string
returnString=Double.toString(result);
if(flag){
return null;
}
// Return result
return returnString;
}else{
return null;
}
}
}
/*********Calculator class***************/
import java.util.Scanner;
/*Calculator class start*/
public class Calculator {
public static void main(String args[]){
/*Variable declaration*/
String expression;
/*Scanner object for input*/
Scanner input=new Scanner(System.in);
/*Prompt for expression*/
System.out.println("Please Enter expression");
expression=input.nextLine();
input.close();
/*Calling Evaluate method*/
String result=P3.evaluate(expression);
/*Printing result if it is not null*/
if(result!=null) {
System.out.println(result);
}
}
}

4. /***************output************/
Please Enter expression
11.22 + 3.456 =
11.22 + 3.456 =14.676
Please Enter expression
5.555 - 32.14 =
5.555 - 32.14 =-26.585
Please Enter expression
25634.8 * .32 =
25634.8 * .32 = 8203.136
Please Enter expression
5 ^ 4 =
5 ^ 4 =625.0
Please Enter expression
Whatever + 2 =
Whatever + 2 =Invalid Operand
Please Enter expression
4.0 - 1.2.3 =
4.0 - 1.2.3 =Invalid Operand
Please Enter expression
1.234 $ 0.5 =
1.234 $ 0.5 =Invalid Operator
Thanks a lot
Solution
//Tested on Eclipse and both class should be in same package
import java.util.Scanner;
public class P3 {
/*isInteger method implementation
* @param String type
* while parsing if it throw exception then it is not integer
* else it is integer*/
public static Boolean isDouble(String token){
try {
Double.parseDouble(token);

5. } catch(NumberFormatException e) {
System.out.println("Invalid Operand");
return false;
} catch(NullPointerException e) {
System.out.println("Invalid Operand");
return false;
}
// only got here if we didn't return false
return true;
}
public static String evaluate(String expression) {
// Print expression
System.out.print(expression);
// Declare variables for operands, operator, result, and return value
double operand1=0,operand2 = 0,result=0;
char operator;
Boolean flag=Boolean.FALSE;//for if operators were not listed
String returnString = "";
String token[]=new String[expression.length()];//for storing all token from expression
// Create Scanner object to parse expression
// create a new scanner with the specified String Object
int i=0;
Scanner scanner = new Scanner(expression);
while(scanner.hasNext()){
token[i]=scanner.next();
i++;
}
scanner.close();
// Compute a numerical result for the expression
if(isDouble(token[0])){
operand1=Double.parseDouble(token[0]);
}
if(isDouble(token[2])){
operand2=Double.parseDouble(token[2]);
}
operator=token[1].charAt(0);

6. if(operand1!=0&&operand2!=0){
switch(operator){
case '+':
result=operand1+operand2;
break;
case '-':
result=operand1-operand2;
break;
case '*':
result=operand1*operand2;
break;
case '/':
result=operand1/operand2;
break;
case '%':
result=operand1%operand2;
break;
case '^':
result=Math.pow(operand1, operand2);
break;
default:
System.out.println("Invalid Operator");
flag=Boolean.TRUE;
break;
}
// Convert numerical result to string
returnString=Double.toString(result);
if(flag){
return null;
}
// Return result
return returnString;
}else{
return null;
}

7. }
}
/*********Calculator class***************/
import java.util.Scanner;
/*Calculator class start*/
public class Calculator {
public static void main(String args[]){
/*Variable declaration*/
String expression;
/*Scanner object for input*/
Scanner input=new Scanner(System.in);
/*Prompt for expression*/
System.out.println("Please Enter expression");
expression=input.nextLine();
input.close();
/*Calling Evaluate method*/
String result=P3.evaluate(expression);
/*Printing result if it is not null*/
if(result!=null) {
System.out.println(result);
}
}
}
/***************output************/
Please Enter expression
11.22 + 3.456 =
11.22 + 3.456 =14.676
Please Enter expression
5.555 - 32.14 =
5.555 - 32.14 =-26.585
Please Enter expression
25634.8 * .32 =
25634.8 * .32 = 8203.136
Please Enter expression

8. 5 ^ 4 =
5 ^ 4 =625.0
Please Enter expression
Whatever + 2 =
Whatever + 2 =Invalid Operand
Please Enter expression
4.0 - 1.2.3 =
4.0 - 1.2.3 =Invalid Operand
Please Enter expression
1.234 $ 0.5 =
1.234 $ 0.5 =Invalid Operator
Thanks a lot