Evaluate Postfix Notation Entered From Keyboard?
Oct 24, 2014
My question is to evaluate a Postfix notation entered from keyboard. I have no errors in my code but it prints only :
Exception in thread "main"
java.util.NoSuchElementException
at ArrayStack.pop(PostFixEvaluation.java:72)
at PostFixEvaluation.evaluatePostfix(PostFixEvaluatio n.java:107)
at PostFixEvaluation.main(PostFixEvaluation.java:140)
I tried many values but it prints the same exception all the time.
Here is my code:
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.NoSuchElementException;
interface Stack<E> {
[Code] ....
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Apr 7, 2014
So I am supposed to be changing infix notation to postfix notation using stacks. This is simply taking a string "3 + 5 * 6" (infix) and turning it into (3 5 6 * +" (postfix).
To do this, we are to scan the string from left to right and when we encounter a number, we just add it to the final string, but when we encounter an operand, we throw it on the stack. Then if the next operand has a higher input precedence than the stack precedence of the operator on the top of the stack, we add that operator to the stack too, otherwise we pop from the stack THEN add the new operator.
I am supposed to be utilizing a hash map but I don't see how you would go about doing this. We are supposed to store operators on the hash map but operators need their own character, input precedence, stack precedence, and rank. How do you use a hash map when you need to tie a character to 3 values instead of just 1? I just don't get it.
The following is our Operator class that we are to use. Another problem is this isn't really supposed to be modified, yet we were given two important variables (inputPrecedence and outputPrecedence) that we can't have nothing to be initialized to and no way of accessing? So that might be where a hash map comes in but I am not sure. I am not very sure on how they exactly work anyway...
public class Operator implements Comparable<Operator>
{
public char operator; // operator
privateint inputPrecedence; // input precedence of operator in the range [0, 5]
privateint stackPrecedence; // stack precedence of operator in the range [-1, 3]
[Code] ....
So my question mostly revolves around how I tie an Operator character to its required values, so I can use it in my code to test two operators precedence values.
My original thought was turn string into character array, but then I would need nested for/while loops to check if it is a number or letter, or if it is an operator and thus result in O(n^2) time
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This is what i have done already which works, but i need to ignore the negative number when print out max and min...which i dont know how to do so. when i compile this program now it will always give me the negative number i enter at the end as minimum. which i need to ignore
Also if negative number is entered at once the program should print a error message say max and min are undefined.
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int large = Integer.MIN_VALUE;
int small = Integer.MAX_VALUE;
while(true) {
System.out.print("Enter a integer: ");
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[Code] ....
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package hw10;
public class Node {
String value;
Node left, right;
public Node(String value) {
[Code] .....
When i test my code, some trouble like this:
Enter a prefix expression: - + 10 * 2 8 3
prefix expression:
- + 10 * 2 8 3
postfix expression:
+ 10 * 2 8 3 -
infix expression:
( ( 10 + ( 2 * 8 ) ) - 3 )
[Code] .....
the error lines:
75: double left = evaluate(node.left);
107: evaluate(root);
In the Instruction, which said:
- int evaluate(Node node)
Given the root node of an expression tree, evaluates the expression using post-order traversal and returns the answer. main method Testing logic.
And I found the postfix expression was wrong, it should be: 10 2 8 * + 3 -
I think maybe the tree's order had some problems result in these cases or...
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[Code] .....
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(ii) 4 assignment , 1 multiplication , 2 addition
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May i know is my answer is correct ??
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[Code] .....
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for(j = 0; j < n; j++)
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Java Code:
public class MountainBike extends Bicycle {
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[Code] ....
At first,
Java Code: public int seatHeight; mh_sh_highlight_all('java');
tells us that seatHeight is NOT a static field (because of the absence of static keyword).
Whereas in the constructor, the absence of dot notation (like something like this.seatHeight) in
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So I am working on a PostFix calculator that is used in command line for a class project, and I am having a little trouble on developing a memory for it. I have been told to create a hashMap and I have researched it and understand the basics of it. I have the calculating method working, but what I am having trouble trying to implement a way for the user to declare variables. For example this what the user should be able to do:
> a = 3 5 + 1 -
7
> bee = a 3 *
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> a bee +
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[code]....
I just need to be able to save the answers as a variable the User names, such as the example and let the user be able to use the variables later.
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public static String evaluate(String input) {
char[] a = input.toCharArray();
if (input.isEmpty())
return "No input";
else if (input.equals(" "))
return "No input";
else if (input.equals(" "))
[code]....
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Will the postfix x++ and the prefix --y change the answer for this question?
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Nov 24, 2014
I need to convert infix To Postfix but have a few errors.
Error msg:
PostFix:
Exception in thread "main" java.util.EmptyStackException
at java.util.Stack.peek(Unknown Source)
at java.util.Stack.pop(Unknown Source)
at assignment4.infixToPostfix.evaluatePostfix(infixTo Postfix.java:129)
at assignment4.infixToPostfix.main(infixToPostfix.jav a:19)
NB:
129 >>return (double) s1.pop(); AND 19>>>double ans = evaluatePostfix(postfixStr);
Deadline = less than 1 hour
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import java.util.*;
public class stack {
public static char[] convertToPostfix(char[] infixEx) {
Stack<Character> operatorStack = new Stack<Character>();
char[] postfix = new char[infixEx.length];
int index = 0;
[Code] .....
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My verify method also always returns false. So I'm given three classes to begin with. Calculator, Expression, and InfixExpression and they are listed below.
The goal is to create a class called PostfixExpression that extends Expression and can read and calculate postfix expressions.
My evaluate() method works for most calculations but when it needs to return a negative value it just returns the positive equivalent.
Also, my verify method always returns false and I can't pinpoint why.
Here's my current code. Some things are commented out for debugging purposes.
import java.util.Scanner;
/**
* Simple calculator that reads infix expressions and evaluates them.
*/
public class Calculator
{
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
[Code] .....
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Apr 13, 2015
package hw9;
import java.util.Scanner;
import java.util.Stack;
public class stack {
public static Integer evaluate(String expression) {
Scanner scanner = new Scanner(expression);
Stack <Integer> operands = new Stack<Integer>();
[Code] ....
When I input my expression which has spaces between characters e.g.:10 2 8 * + 3 -, it worked; when I put expression which may not add space between each char e.g.: 3 14+2*7/, the error showed:
Enter a postfix expression: 3 14+2*7/
Exception in thread "main" java.util.EmptyStackException
at java.util.Stack.peek(Stack.java:102)
at java.util.Stack.pop(Stack.java:84)
at hw9.stack.evaluate(stack.java:22)
at hw9.stack.main(stack.java:45)
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Here is my code for that segment:
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[Code] .....
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[Code].....
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The program should read the name of the file from the keyboard.
************************************************** ************************************************** **************
I need to get the filename from the user for this particular program. Usually I would have the name of the file prewritten into the source code like this....
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I tried different ways but I just can't seem to figure it out.... I guess what I'm really asking is how to rearrange Scanner input = new Scanner(new File("gettsy_burg.txt"); since I want the user to input the filename instead of the filename being prewritten by the programmer(me).
This is what I have so far to let the user for input....
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