Infix Expression Calculation

This program provides another and cases of the application of the Stack besides what I had mentioned in a previous a Rticle:

(1) Class infixexpr converts an Infix expression to a Suffix expression by using a operator stack;

(2) Class Suffix calculates the value of a Suffix expression by using a stack containing operands.

　　Sample Input and Output:

　　

1 ImportJava.util.*;2 ImportJava.io.*;3 4 classSuffix {5     PrivateStack<integer>Stack;6     7      PublicSuffix () {8stack =NewStack<integer>();9     }Ten      Public voidAddtoken (String str) { One         if(Str.equals ("+") | | str.equals ("-") | | str.equals ("*") | | AStr.equals ("/") | | Str.equals ("^")) { -             intb =Stack.pop (). Intvalue (); -             intA =Stack.pop (). Intvalue (); the             if(Str.equals ("+")) { -Stack.add (NewInteger (A +b)); -}Else if(Str.equals ("-")) { -Stack.add (NewInteger (A-b)); +}Else if(Str.equals ("*")) { -Stack.add (NewInteger (A *b)); +}Else if(Str.equals ("/")) { AStack.add (NewInteger (A/b)); at}Else { -                 intval = 1; -                  for(inti=0;i<b;i++) { -Val *=A; -                 } -Stack.add (NewInteger (Val)); in             } -}Else{//An operand to Stack.add (integer.valueof (str)); +         } -     } the      Public intGetval () { *         returnStack.peek (). Intvalue (); $     }Panax Notoginseng      Public voidClear () { - stack.clear (); the     } + } A  the  Public classinfixexpr { +     Private StaticBufferedReader in; -     Private StaticStringTokenizer Tokenizer; $     Private StaticStack<string>Stack; $     Private StaticSuffix server; -      -     Private Static voidprintandcal (String expr) { the System.out.println (expr); -Tokenizer =NewStringTokenizer (expr);Wuyi         //Attention:we can ' t use a for-loop based on the         //Tokenizer.counttokens () since it is mutable -          while(Tokenizer.hasmoretokens ()) { WuString str =Tokenizer.nexttoken (); -             if(Str.equals ("(")) { About Stack.add (str); $}Else if(Str.equals (")")) { -String op =Stack.pop (); -                  while(!op.equals ("(")) { - Server.addtoken (OP); AOP =Stack.pop (); +                 } the}Else if(Str.equals ("+") | | str.equals ("-") | | str.equals ("*") | | -Str.equals ("/") | | Str.equals ("^")) { $                  while(!stack.isempty () &&!stack.peek (). Equals ("(") &&Prior (Stack.peek (), str)) { the Server.addtoken (Stack.pop ()); the                 } the Stack.add (str); the}Else{//An operand - Server.addtoken (str); in             } the         } the          while(!Stack.isempty ()) { About Server.addtoken (Stack.pop ()); the         } the System.out.println (Server.getval ()); the     } +     Private Static BooleanPrior (String op1,string op2) { -         //Returns Whether OP1 can be operated first the         //It is aligned with operator OP2Bayi         if(Op2.equals ("^")) { the             return false; the}Else if(Op2.equals ("*") | | Op2.equals ("/")) { -             return!op1.equals ("+") &&!op1.equals ("-")); -}Else {     the             return true; the         } the     } the      Public Static voidMain (string[] args)throwsIOException { -in =NewBufferedReader (NewFileReader ("Infix.in")); thestack =NewStack<string>(); theServer =NewSuffix (); the         intn =Integer.parseint (In.readline ());94 System.out.println (n); the          for(inti=0;i<n;i++) { the server.clear (); the printandcal (In.readline ());98         } About in.close (); -     }101}

Infix Expression Calculation