Java inverse Polish Algorithm

Package expression;

Import java. Io .*;
Import java. util .*;

Public class expression {
Private arraylist expression = new arraylist (); // stores the ordinal expression

Private arraylist right = new arraylist (); // stores the right-order expression

Private string result; // result

// Create an object based on input information and put the values and operators into arraylist
Private expression (string input ){
Stringtokenizer ST = new stringtokenizer (input, "+-*/()", true );
While (St. hasmoreelements ()){
Expression. Add (St. nexttoken ());
}
}

// Convert the intermediate expression to the right expression
Private void toright (){
Stacks astack = new stacks ();
String operator;
Int position = 0;
While (true ){
If (calculate. isoperator (string) expression. Get (position ))){
If (astack. Top =-1
| (String) expression. Get (position). Equals ("(")){
Astack. Push (expression. Get (position ));
} Else {
If (string) expression. Get (position). Equals (")")){
If (! (String) astack. Top (). Equals ("(")){
Operator = (string) astack. Pop ();
Right. Add (operator );
}
} Else {
If (calculate. Priority (string) Expression
. Get (position) <= calculate
. Priority (string) astack. Top ())
& Astack. Top! =-1 ){
Operator = (string) astack. Pop ();
If (! Operator. Equals ("("))
Right. Add (operator );
}
Astack. Push (expression. Get (position ));
}
}
} Else
Right. Add (expression. Get (position ));
Position ++;
If (position> = expression. Size ())
Break;
}
While (astack. Top! =-1 ){
Operator = (string) astack. Pop ();
Right. Add (operator );
}
}

// Evaluate the right-order expression
Private void getresult (){
This. toright ();
Stacks astack = new stacks ();
String OP1, OP2, is = NULL;
Iterator it = right. iterator ();

While (it. hasnext ()){
Is = (string) it. Next ();
If (calculate. isoperator (is )){
OP1 = (string) astack. Pop ();
OP2 = (string) astack. Pop ();
Astack. Push (calculate. tworesult (is, OP1, OP2 ));
} Else
Astack. Push (is );
}
Result = (string) astack. Pop ();
It = expression. iterator ();
While (it. hasnext ()){
System. Out. Print (string) it. Next ());
}
System. Out. println ("=" + result );
}

Public static void main (string AVG []) {
Try {
System. Out. println ("input a expression :");
Bufferedreader is = new bufferedreader (New inputstreamreader (
System. In ));
For (;;){
String input = new string ();
Input = is. Readline (). Trim ();
If (input. Equals ("Q "))
Break;
Else {
Expression Boya = new expression (input );
Boya. getresult ();
}
System. Out
. Println ("input another expression or input 'q' to quit :");
}
Is. Close ();
} Catch (ioexception e ){
System. Out. println ("wrong input !!! ");
}
}
}

 

Java code
Package expression;

Public class calculate {
// Determine whether it is an operator symbol
Public static Boolean isoperator (string operator ){
If (operator. Equals ("+") | Operator. Equals ("-")
| Operator. Equals ("*") | Operator. Equals ("/")
| Operator. Equals ("(") | Operator. Equals (")"))
Return true;
Else
Return false;
}

// Set the priority of the operation symbol
Public static int priority (string operator ){
If (operator. Equals ("+") | Operator. Equals ("-")
| Operator. Equals ("("))
Return 1;
Else if (operator. Equals ("*") | Operator. Equals ("/"))
Return 2;
Else
Return 0;
}

// Perform calculation between two values
Public static string tworesult (string operator, string a, string B ){
Try {
String op = operator;
String rs = new string ();
Double X = double. parsedouble (B );
Double Y = double. parsedouble ();
Double Z = 0;
If (op. Equals ("+ "))
Z = x + y;
Else if (op. Equals ("-"))
Z = x-y;
Else if (op. Equals ("*"))
Z = x * Y;
Else if (op. Equals ("/"))
Z = x/y;
Else
Z = 0;
Return Rs + z;
} Catch (numberformatexception e ){
System. Out. println ("input has something wrong! ");
Return "error ";
}
}
}

Java code
Package expression;
Import java. util .*;
// Stack
Public class stacks {
Private partition list = new partition list ();
Int Top =-1;
Public void push (object Value ){
Top ++;
List. addfirst (value );
}
Public object POP (){
Object temp = List. getfirst ();
Top --;
List. removefirst ();
Return temp;

}
Public object top (){
Return list. getfirst ();
}
}