A small program that computes the plural arithmetic operations

// The input format of the application is:
// * 3 + 4I 5 + 8i
// Operator + N spaces + the first plural number + N spaces + the second plural number
/*
* Auther starshus
*
* Date 04/11/20
*/
Import java. Io. bufferedreader;
Import java. Io. inputstreamreader;
// 5.7.10
Public class command
{
Private string CommandLine;
Public command (string line) // constructor to obtain the input
{
CommandLine = line. Trim (); //. Trim () is used to remove spaces on both sides.
}
Public String getcommand () // get an operator in + ,-, *,/
{
String cmd = "";
Int Index = CommandLine. indexof ('');
If (index> = 0)
Cmd = CommandLine. substring (0, index );
Else cmd = CommandLine;
Return cmd; //. touppercase ();
}
// Assume that the input format is + A + bi C + DI
// Extract the number a first
Public String geta ()
{
String A = "";
Int index1 = CommandLine. indexof ('');
If (index1> = 0)
{
A = CommandLine. substring (index1 + 1, CommandLine. Length (). Trim ();
Int index2 = A. indexof ('');
If (index2> = 0)
A = A. substring (0, index2 );
Int index3 = A. indexof ('+ ');
If (index3> = 0)
A = A. substring (0, index3 );
} Else a = "";
Return;
}
// Extract B
Public String getb ()
{
String B = "";
Int index1 = CommandLine. indexof ('');
If (index1> = 0)
{
B = CommandLine. substring (index1 + 1, CommandLine. Length (). Trim ();
Int index2 = B. indexof ('');
If (index2> = 0)
B = B. substring (0, index2 );
Int index3 = B. indexof ('+ ');
Int index4 = B. indexof ('I ');
If (index3 + 1) = index4)
{
B = "1 ";
Return B;
}
Else if (index3> = 0 & index4> = 0)
B = B. substring (index3 + 1, index4 );
Else
B = "0 ";
} Else B = "";
Return B;
}
// Extract C
Public String GETC ()
{
String c = "";
Int index1 = CommandLine. indexof ('');
If (index1> = 0)
{
C = CommandLine. substring (index1 + 1, CommandLine. Length (). Trim ();
Int index2 = C. indexof ('');
If (index2> = 0)
C = C. substring (index2 + 1, C. Length (). Trim ();
Int index3 = C. indexof ('+ ');
If (index3> = 0)
C = C. substring (0, index3 );
} Else c = "";
Return C;
}
// Extract d
Public String getd ()
{
String d = "";
Int index1 = CommandLine. indexof ('');
If (index1> = 0)
{
D = CommandLine. substring (index1 + 1, CommandLine. Length (). Trim ();
Int index2 = D. indexof ('');
If (index2> = 0)
D = D. substring (index2 + 1, D. Length (). Trim ();
Int index3 = D. indexof ('+ ');
Int index4 = D. indexof ('I ');
If (index3 + 1) = index4)
{
D = "1 ";
Return D;
}
Else if (index3> = 0 & index4> = 0)
D = D. substring (index3 + 1, index4 );
Else
D = "0 ";
} Else d = "";
Return D;
}
Public static string add (double A, double B, double C, double D) // Addition
{
Double realpart, imaginarypart;
Realpart = A + C;
Imaginarypart = B + D;
If (imaginarypart> 0)
Return (realpart + "+" + imaginarypart + "I ");
Else
Return (realpart + "" + imaginarypart + "I ");
}
Public static string sub (double A, double B, double C, double D) // Subtraction
{
Double realpart, imaginarypart;
Realpart = A-C;
Imaginarypart = B-d;
If (imaginarypart> 0)
Return (realpart + "+" + imaginarypart + "I ");
Else
Return (realpart + "" + imaginarypart + "I ");
}
Public static string mult (double A, double B, double C, double D) // Multiplication
{
Double realpart, imaginarypart;
Realpart = A * C-B * D;
Imaginarypart = A * D + B * C;
If (imaginarypart> 0)
Return (realpart + "+" + imaginarypart + "I ");
Else
Return (realpart + "" + imaginarypart + "I ");
}
Public static string Division (double A, double B, double C, double D) // Division
{
Double realpart, imaginarypart;
Realpart = (A * C + B * D)/(c * C + D * D );
Imaginarypart = (B * C-A * D)/(c * C + D * D );
If (imaginarypart> 0)
Return (realpart + "+" + imaginarypart + "I ");
Else
Return (realpart + "" + imaginarypart + "I ");
}
Public static void main (string [] ARGs) // master Method
{
System. Out. println ("Welcome! Press 'q' or 'q' to quit .");
System. Out. println ("You can use this program like the follow example :");
System. Out. println ("* 20 + 30i 15 + 35i ");
System. Out. println ("+ 20 +-30i 15 +-35i ");
System. Out. println ("the first character can be '*' or '/' or '+' or '-'.");
For (;;)
{
System. Out. Print ("$ ");
String inputline;
Try {
Bufferedreader in = new bufferedreader (New inputstreamreader (system. In ));
Inputline = in. Readline ();
} Catch (exception exc ){
System. Out. println ("your input can't be used .");
Continue;
}
Command commander = new command (inputline); // use the command class to generate an object
String cmd = commander. getcommand ();
If (CMD. Equals ("Q") | cmd. Equals ("Q "))
Break;
Else if (CMD. equals ("+") | cmd. equals ("-") | cmd. equals ("*") | cmd. equals ("/"))
{
Double A1, B1, C1, D1;
Try {
String A = commander. Geta ();
A1 = double. valueof (a). doublevalue ();
String B = commander. getb ();
B1 = double. valueof (B). doublevalue ();
String c = commander. GETC ();
C1 = double. valueof (c). doublevalue ();
String d = commander. getd ();
D1 = double. valueof (d). doublevalue ();
} Catch (exception exc ){
System. Out. println ("sorry, your input can't be used .");
System. Out. println ("It shoshould be looks like: * 1 + 2I 3 + 4I ");
Continue;
}
If (CMD. Equals ("+ "))
{
System. Out. println ("the result is:" + Add (A1, B1, C1, D1 ));
}
Else if (CMD. Equals ("-"))
{
System. Out. println ("the result is:" + sub (A1, B1, C1, D1 ));
}
Else if (CMD. Equals ("*"))
{
System. Out. println ("the result is:" + mult (A1, B1, C1, D1 ));
}
Else if (CMD. Equals ("/"))
{
System. Out. println ("the result is:" + division (A1, B1, C1, D1 ));
}
} Else
System. Out. println ("sorry, the first character can be '*' or '/' or '+' or '-'.");
}
}

}