Java计算对象大小的方法详解

import jdk.nashorn.internal.ir.debug.ObjectSizeCalculator;
import lombok.extern.slf4j.Slf4j;

@Slf4j
public class ObjectCalculatorTest {
    public static void main(String[] args) {
        String text = "Hello World!"; //12 chars
        Long objectSizeBytes = ObjectSizeCalculator.getObjectSize(text);
        log.info("objectSizeBytes: {} bytes", objectSizeBytes );//64 bytes

        Integer number = new Integer(11);
        objectSizeBytes = ObjectSizeCalculator.getObjectSize(number);
        log.info("objectSizeBytes: {} bytes", objectSizeBytes );//16 bytes

		Map<String, String> map = new HashMap<>();
        objectSizeBytes = ObjectSizeCalculator.getObjectSize(number);
        log.info("objectSizeBytes: {} bytes", objectSizeBytes );//48 bytes
    }
}

<dependency>
	<groupId>org.apache.lucene</groupId>
	<artifactId>lucene-core</artifactId>
	<version>8.7.0</version>
</dependency>

import lombok.extern.slf4j.Slf4j;
import org.apache.lucene.util.RamUsageEstimator;

@Slf4j
public class ObjectCalculatorTest {
    public static void main(String[] args) {
        String text = "Hello World!"; //12 char = 12 byte
        objectSizeBytes = RamUsageEstimator.shallowSizeOf( text );
        log.info("objectSizeBytes: {} bytes", objectSizeBytes );//24 bytes
		
    	Integer number = new Integer(11);
        System.out.println(RamUsageEstimator.shallowSizeOf(number));//16 bytes

		Map<String, String> map = new HashMap<>();
		System.out.println(RamUsageEstimator.shallowSizeOf(map));//48 bytes
    }
}

    /**
     * The value of the {@code Integer}.
     *
     * @serial
     */
    private final int value;

transient Set<K>        keySet;
transient Collection<V> values;

transient Node<K,V>[] table;
transient Set<Map.Entry<K,V>> entrySet;
transient int size;
transient int modCount;
int threshold;
final float loadFactor;