Is there any sizeof-like method in Java?

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

yes..in JAVA

System.out.println(Integer.SIZE/8);  //gives you 4.
System.out.println(Integer.SIZE);   //gives you 32.

//Similary for Byte,Long,Double....

Answer 2

You can do bit manipulations like below to obtain the size of primitives:

public int sizeofInt() {
    int i = 1, j = 0;
    while (i != 0) {
        i = (i<<1); j++;
    }
    return j;
}

public int sizeofChar() {
    char i = 1, j = 0;
    while (i != 0) {
        i = (char) (i<<1); j++;
    }
    return j;
}

Answer 3

Just some testing about it:

public class PrimitiveTypesV2 {

public static void main (String[] args) {
    Class typesList[] = {
            Boolean.class , Byte.class, Character.class, Short.class, Integer.class,
            Long.class, Float.class, Double.class, Boolean.TYPE, Byte.TYPE, Character.TYPE,
            Short.TYPE, Integer.TYPE, Long.TYPE, Float.TYPE, Double.TYPE
        };
    
    try {               
        for ( Class type : typesList ) {
            if (type.isPrimitive()) {
                System.out.println("Primitive type:\t" + type); 
            }
            else {
                boolean hasSize = false;
                java.lang.reflect.Field fields[] = type.getFields();
                for (int count=0; count<fields.length; count++) {
                    if (fields[count].getName().contains("SIZE")) hasSize = true;
                }
                if (hasSize) {
                    System.out.println("Bits size of type " + type + " :\t\t\t" + type.getField("SIZE").getInt(type) );
                    double value = type.getField("MIN_VALUE").getDouble(type);
                    long longVal = Math.round(value);
                    if ( (value - longVal) == 0) {
                        System.out.println("Min value for type " + type + " :\t\t" + longVal );
                        longVal = Math.round(type.getField("MAX_VALUE").getDouble(type));
                        System.out.println("Max value for type " + type + " :\t\t" + longVal );
                    }
                    else {
                        System.out.println("Min value for type " + type + " :\t\t" + value );
                        value = type.getField("MAX_VALUE").getDouble(type);
                        System.out.println("Max value for type " + type + " :\t\t" + value );
                    }
                }
                else {
                    System.out.println(type + "\t\t\t type without SIZE field.");
                }
            } // if not primitive
        } // for typesList
    } catch (Exception e) {e.printStackTrace();}
} // main
} // class PrimitiveTypes

Answer 4

EhCache provides a SizeOf class that will try to use the Instrumentation agent and will fall back to a different approach if the agent is not loaded or cannot be loaded (details here).

Also see the agent from Heinz Kabutz.

Answer 5

There's a class/jar available on SourceForge.net that uses Java instrumentation to calculate the size of any object. Here's a link to the description: java.sizeOf

Answer 6

You can use Integer.SIZE / 8, Double.SIZE / 8, etc. for primitive types from Java 1.5.