Java Example - Converting Infix Expression to Postfix Expression Using Stack
The following example demonstrates how to use a stack to convert an infix expression to a postfix expression:
InToPost.java File
import java.io.IOException;
public class InToPost {
private Stack theStack;
private String input;
private String output = "";
public InToPost(String in) {
input = in;
int stackSize = input.length();
theStack = new Stack(stackSize);
}
public String doTrans() {
for (int j = 0; j < input.length(); j++) {
char ch = input.charAt(j);
switch (ch) {
case '+':
case '-':
gotOper(ch, 1);
break;
case '*':
case '/':
gotOper(ch, 2);
break;
case '(':
theStack.push(ch);
break;
case ')':
gotParen(ch);
break;
default:
output = output + ch;
break;
}
}
while (!theStack.isEmpty()) {
output = output + theStack.pop();
}
System.out.println(output);
return output;
}
public void gotOper(char opThis, int prec1) {
while (!theStack.isEmpty()) {
char opTop = theStack.pop();
if (opTop == '(') {
theStack.push(opTop);
break;
}
else {
int prec2;
if (opTop == '+' || opTop == '-')
prec2 = 1;
else
prec2 = 2;
if (prec2 < prec1) {
theStack.push(opTop);
break;
}
else
output = output + opTop;
}
}
theStack.push(opThis);
}
public void gotParen(char ch){
while (!theStack.isEmpty()) {
char chx = theStack.pop();
if (chx == '(')
break;
else
output = output + chx;
}
}
public static void main(String[] args)
throws IOException {
String input = "1+2*4/5-7+3/6";
String output;
InToPost theTrans = new InToPost(input);
output = theTrans.doTrans();
System.out.println("Postfix is " + output + '\n');
}
}
String output = theTrans.doTrans();
System.out.println("Postfix is " + output + '\n');
}
class Stack {
private int maxSize;
private char[] stackArray;
private int top;
public Stack(int max) {
maxSize = max;
stackArray = new char[maxSize];
top = -1;
}
public void push(char j) {
stackArray[++top] = j;
}
public char pop() {
return stackArray[top--];
}
public char peek() {
return stackArray[top];
}
public boolean isEmpty() {
return (top == -1);
}
}
}
The above code outputs the following result:
124*5/+7-36/+
Postfix is 124*5/+7-36/+
Java Examples ```