How to write a C like sizeof() function in Java? [Solved]

In Java, you cannot directly access the size of an object or a primitive type like you can with the sizeof() function in C. 

The sizeof() function in C returns the size in bytes of a given type or object. However, you can use the java.lang.instrument.Instrumentation class to approximate the size of an object in Java. 

Here's an example of how you can write a function similar to sizeof() in Java using the Instrumentation class:

import java.lang.instrument.Instrumentation;

public class SizeOfUtil {
    private static Instrumentation instrumentation;

    public static void premain(String agentArgs, Instrumentation inst) {
        instrumentation = inst;
    }

    public static long sizeOf(Object obj) {
        if (instrumentation == null) {
            throw new IllegalStateException("Instrumentation not initialized");
        }
        return instrumentation.getObjectSize(obj);
    }
}

To use this SizeOfUtil class, you need to run your Java application with the -javaagent command-line option, specifying the JAR file containing SizeOfUtil as the agent. For example:

java -javaagent:sizeofutil.jar YourMainClass

Make sure to replace sizeofutil.jar with the actual name of the JAR file containing SizeOfUtil. Now, in your code, you can call the sizeOf() function to get an approximation of the size of an object. Here's an example:

public class Main {
    public static void main(String[] args) {
        SizeOfUtil.premain("", null);

        int[] arr = new int[1000];
        long size = SizeOfUtil.sizeOf(arr);
        System.out.println("Size of arr: " + size + " bytes");
    }
}

Please note that this approach provides an approximation of the size of an object and may not be 100% accurate due to various factors like JVM optimizations and object alignment.