Implementation of Infix to Postfix Expression Converter

Java/stack/InfixToPostfixConverter.java

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+// Hacktoberfest 2025 Contribution
+// Description: Java Program to convert an Infix expression to Postfix using Stack (OOP based)
+
+import java.util.Stack;
+
+public class InfixToPostfixConverter {
+
+    // Function to check if a character is an operand (A-Z or a-z or digit)
+    private boolean isOperand(char c) {
+        return Character.isLetterOrDigit(c);
+    }
+
+    // Function to return precedence of operators
+    private int precedence(char ch) {
+        switch (ch) {
+            case '+':
+            case '-':
+                return 1;
+            case '*':
+            case '/':
+                return 2;
+            case '^':
+                return 3;
+        }
+        return -1;
+    }
+
+    // Main conversion function
+    public String infixToPostfix(String expression) {
+        StringBuilder result = new StringBuilder();
+        Stack<Character> stack = new Stack<>();
+
+        for (int i = 0; i < expression.length(); i++) {
+            char c = expression.charAt(i);
+
+            // If the scanned character is an operand, add it to the output
+            if (isOperand(c)) {
+                result.append(c);
+            }
+            // If the scanned character is '(', push it to stack
+            else if (c == '(') {
+                stack.push(c);
+            }
+            // If the scanned character is ')', pop until '(' is found
+            else if (c == ')') {
+                while (!stack.isEmpty() && stack.peek() != '(') {
+                    result.append(stack.pop());
+                }
+                stack.pop(); // remove '('
+            }
+            // Operator encountered
+            else {
+                while (!stack.isEmpty() && precedence(c) <= precedence(stack.peek())) {
+                    result.append(stack.pop());
+                }
+                stack.push(c);
+            }
+        }
+
+        // Pop all remaining operators from the stack
+        while (!stack.isEmpty()) {
+            result.append(stack.pop());
+        }
+
+        return result.toString();
+    }
+
+    // Main function for testing
+    public static void main(String[] args) {
+        InfixToPostfixConverter converter = new InfixToPostfixConverter();
+
+        // Sample expressions
+        String infix1 = "A+B*C";
+        String infix2 = "(A+B)*C";
+        String infix3 = "A+(B*C-(D/E^F)*G)*H";
+
+        System.out.println("Infix : " + infix1);
+        System.out.println("Postfix: " + converter.infixToPostfix(infix1));
+
+        System.out.println("\nInfix : " + infix2);
+        System.out.println("Postfix: " + converter.infixToPostfix(infix2));
+
+        System.out.println("\nInfix : " + infix3);
+        System.out.println("Postfix: " + converter.infixToPostfix(infix3));
+    }
+}