Question

Is there any built-in method in Java to find the size of any datatype?
Is there any way to find size?

Answer 1

No. There is no such method in the standard Java SE class library.

The designers’ view is that it is not needed in Java, since the language removes the need for an application¹ to know about how much space needs to be reserved for a primitive value, an object or an array with a given number of elements.

You might think that a sizeof operator would be useful for people that need to know how much space their data structures take. However you can also get this information and more, simply and reliably using a Java memory profiler, so there is no need for a sizeof method.

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Previous commenters made the point that sizeof(someType) would be more readable than 4. If you accept that readability argument, then the remedy is in your hands. Simply define a class like this …

public class PrimitiveSizes {
    public static int sizeof(byte b) { return 1; } 
    public static int sizeof(short s) { return 2; }
    // etcetera
}

… and statically import it …

import static PrimitiveSizes.*;

Or define some named constants; e.g.

public static final int SIZE_OF_INT = 4;

Or (Java 8 and later) use the Integer.BYTES constant, and so on.

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Why haven’t the Java designers implemented this in standard libraries? My guess is that:

• they don’t think there is a need for it,
• they don’t think there is sufficient demand for it, and
• they don’t think it is worth the effort.

There is also the issue that the next demand would be for a sizeof(Object o) method, which is fraught with technical difficulties.

The key word in the above is "they"!

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^{1 – A programmer may need to know in order to design space efficient data structures. However, I can’t imagine why that information would be needed in application code at runtime via a method call.}