$ java -cp jol-samples/target/jol-samples.jar org.openjdk.jol.samples.JOLSample_01_Basic

<dependency>
    <groupId>org.openjdk.jol</groupId>
    <artifactId>jol-core</artifactId>
    <version>put-the-version-here</version>
</dependency>

$ java -jar jol-cli.jar -h
Usage: jol-cli.jar <mode> [optional arguments]*

Available modes:
         estimates: Simulate the class layout in different VM modes.
         externals: Show the object externals: the objects reachable from a given instance.
         footprint: Estimate the footprint of all objects reachable from a given instance
     heapdumpstats: Consume the heap dump and print the most frequent instances.
         internals: Show the object internals: field layout and default contents, object header
            shapes: Dump the object shapes present in JAR files or heap dumps.
   string-compress: Consume the heap dumps and figures out the savings attainable with compressed strings.

$ java -jar jol-cli.jar internals java.util.HashMap
# Running 64-bit HotSpot VM.
# Using compressed oop with 3-bit shift.
# Using compressed klass with 3-bit shift.
# Objects are 8 bytes aligned.
# Field sizes by type: 4, 1, 1, 2, 2, 4, 4, 8, 8 [bytes]
# Array element sizes: 4, 1, 1, 2, 2, 4, 4, 8, 8 [bytes]

Instantiated the sample instance via default constructor.

java.util.HashMap object internals:
OFF  SZ                       TYPE DESCRIPTION               VALUE
  0   8                            (object header: mark)     0x0000000000000005 (biasable; age: 0)
  8   4                            (object header: class)    0x00019828
 12   4              java.util.Set AbstractMap.keySet        null
 16   4       java.util.Collection AbstractMap.values        null
 20   4                        int HashMap.size              0
 24   4                        int HashMap.modCount          0
 28   4                        int HashMap.threshold         0
 32   4                      float HashMap.loadFactor        0.75
 36   4   java.util.HashMap.Node[] HashMap.table             null
 40   4              java.util.Set HashMap.entrySet          null
 44   4                            (object alignment gap)
Instance size: 48 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total

$ java -jar jol-cli.jar externals java.lang.String
# Running 64-bit HotSpot VM.
# Using compressed oop with 3-bit shift.
# Using compressed klass with 3-bit shift.
# Objects are 8 bytes aligned.
# Field sizes by type: 4, 1, 1, 2, 2, 4, 4, 8, 8 [bytes]
# Array element sizes: 4, 1, 1, 2, 2, 4, 4, 8, 8 [bytes]

Instantiated the sample instance via default constructor.

java.lang.String@64cee07d object externals:
     ADDRESS       SIZE TYPE             PATH                           VALUE
   58010a600         16 [C               .value                         []
   58010a610    8923824 (something else) (somewhere else)               (something else)
   58098d0c0         24 java.lang.String                                (object)

Addresses are stable after 1 tries.

$ java -jar jol-cli/target/jol-cli.jar footprint java.lang.Thread
# Running 64-bit HotSpot VM.
# Using compressed oop with 3-bit shift.
# Using compressed klass with 3-bit shift.
# Objects are 8 bytes aligned.
# Field sizes by type: 4, 1, 1, 2, 2, 4, 4, 8, 8 [bytes]
# Array element sizes: 4, 1, 1, 2, 2, 4, 4, 8, 8 [bytes]

Instantiated the sample instance via default constructor.

java.lang.Thread@64cee07d footprint:
COUNT       AVG       SUM   DESCRIPTION
   13        84      1104   [B
  496        67     33400   [C
  139        23      3272   [Ljava.lang.Class;
   17        89      1520   [Ljava.lang.Object;
 ...
    1        24        24   sun.reflect.generics.tree.ClassSignature
    3        16        48   sun.reflect.generics.tree.ClassTypeSignature
    2        24        48   sun.reflect.generics.tree.FormalTypeParameter
    3        24        72   sun.reflect.generics.tree.SimpleClassTypeSignature
 2849              200416   (total)

$ mvn clean verify