BAEL-1865 - Java Objects Sizes (#4584)

* BAEL-1865 - Java Objects Sizes

* BAEL-1865 - PR fix

core-java/src/main/java/com/baeldung/objectsize/InstrumentationAgent.java

@@ -0,0 +1,18 @@
+package com.baeldung.objectsize;
+
+import java.lang.instrument.Instrumentation;
+
+public class InstrumentationAgent {
+    private static volatile Instrumentation globalInstrumentation;
+
+    public static void premain(final String agentArgs, final Instrumentation inst) {
+        globalInstrumentation = inst;
+    }
+
+    public static long getObjectSize(final Object object) {
+        if (globalInstrumentation == null) {
+            throw new IllegalStateException("Agent not initialized.");
+        }
+        return globalInstrumentation.getObjectSize(object);
+    }
+}

core-java/src/main/java/com/baeldung/objectsize/InstrumentationExample.java

@@ -0,0 +1,59 @@
+package com.baeldung.objectsize;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class InstrumentationExample {
+
+    public static void printObjectSize(Object object) {
+        System.out.println("Object type: " + object.getClass() + ", size: " + InstrumentationAgent.getObjectSize(object) + " bytes");
+    }
+
+    public static void main(String[] arguments) {
+        String emptyString = "";
+        String string = "Estimating Object Size Using Instrumentation";
+        String[] stringArray = { emptyString, string, "com.baeldung" };
+        String[] anotherStringArray = new String[100];
+        List<String> stringList = new ArrayList<>();
+        StringBuilder stringBuilder = new StringBuilder(100);
+        int maxIntPrimitive = Integer.MAX_VALUE;
+        int minIntPrimitive = Integer.MIN_VALUE;
+        Integer maxInteger = Integer.MAX_VALUE;
+        Integer minInteger = Integer.MIN_VALUE;
+        long zeroLong = 0L;
+        double zeroDouble = 0.0;
+        boolean falseBoolean = false;
+        Object object = new Object();
+
+        class EmptyClass {
+        }
+        EmptyClass emptyClass = new EmptyClass();
+
+        class StringClass {
+            public String s;
+        }
+        StringClass stringClass = new StringClass();
+
+        printObjectSize(emptyString);
+        printObjectSize(string);
+        printObjectSize(stringArray);
+        printObjectSize(anotherStringArray);
+        printObjectSize(stringList);
+        printObjectSize(stringBuilder);
+        printObjectSize(maxIntPrimitive);
+        printObjectSize(minIntPrimitive);
+        printObjectSize(maxInteger);
+        printObjectSize(minInteger);
+        printObjectSize(zeroLong);
+        printObjectSize(zeroDouble);
+        printObjectSize(falseBoolean);
+        printObjectSize(Day.TUESDAY);
+        printObjectSize(object);
+        printObjectSize(emptyClass);
+        printObjectSize(stringClass);
+    }
+
+    public enum Day {
+        MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
+    }
+}

core-java/src/main/java/com/baeldung/objectsize/MANIFEST.MF

@@ -0,0 +1 @@
+Premain-class: com.baeldung.objectsize.InstrumentationAgent