Difference Between C++ and Java

Many engineering students learn C or C++ first, in college. When you move to Java, the familiar syntax can hide some important differences, especially around memory and objects. Knowing them avoids confusion, and "Difference Between C++ and Java" is a classic interview question for freshers.

Build Once vs Build per Operating System

This is the biggest difference.

A C++ compiler turns your code into machine code for one processor and operating system. To support Windows, macOS and Linux, you compile three times and ship three different programs.

Java's compiler turns your code into bytecode. You compile once, and the same .class file runs on every operating system that has a JVM.

The Differences Side by Side

Both languages are statically typed, both support object-oriented programming, and both are fast. They just make different trade-offs.

Memory: You vs the Garbage Collector

Here is the same small task in both languages: create three ticket labels and print them.

This is the C++ version. It is for comparison only, so it can't be run here.

#include <iostream>
#include <string>
 
int main() {
    for (int i = 1; i <= 3; i++) {
        std::string* ticket = new std::string("Ticket-" + std::to_string(i));
        std::cout << *ticket << std::endl;
        delete ticket;   // you must free this memory yourself
    }
    return 0;
}

This is the Java version.

public class Tickets {
    public static void main(String[] args) {
        for (int i = 1; i <= 3; i++) {
            String ticket = "Ticket-" + i;
            System.out.println(ticket);
        }
        // No delete needed: the garbage collector frees
        // objects that are no longer used.
    }
}

Ticket-1
Ticket-2
Ticket-3

How it works

1. Line 3 repeats the loop three times, with i taking the values 1, 2 and 3. You'll learn loops in "Java for Loop".
2. Line 4 creates a new String object each time, such as "Ticket-1".
3. Line 5 prints it.
4. There is no delete. When a ticket string is no longer used, Java's garbage collector reclaims its memory automatically.

In the C++ version, forgetting the delete line causes a memory leak, and deleting the same object twice can crash the program. Modern C++ usually avoids raw new and delete by using smart pointers, but the programmer still decides how memory is managed. In Java, you don't.

Try it yourself: change the loop in the Java version to print five tickets instead of three.

Common Mistakes

Assuming Java objects behave like C++ objects on the stack. In Java, every object is created on the heap with new (or a literal like a string), and variables hold references to objects. The lesson "Object References and Null" explains this in detail.

Looking for delete or destructors. Java has neither. Memory is freed by the garbage collector, and resources such as files are closed with try-with-resources.

Saying "Java has no pointers" and stopping there. Java has references, which point to objects. What Java doesn't have is pointer arithmetic or direct access to memory addresses.

Interview Corner

Practice

1. Easy: List three things you can do in C++ that Java doesn't allow.
2. Harder: In the Java version, change the label to "Seat-" and number the seats from 10 to 12 instead of 1 to 3.

Key Takeaways