Class CompactObjectHeadersExamples

java.lang.Object

net.jrodolfo.java_evolution.java25.compact_object_headers.CompactObjectHeadersExamples

public class CompactObjectHeadersExamples
extends Object

Demonstrates the Java 25 Compact Object Headers runtime option.

Compact object headers are JVM implementation details, so this example does not try to measure object sizes. Instead, it launches a child JVM and verifies the executable part that is faithful and portable: Java 25 accepts -XX:+UseCompactObjectHeaders as a product flag, and -XX:+PrintFlagsFinal reports the flag state selected on the command line.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final record	CompactObjectHeadersExamples.VmFlagState	A JVM flag state reported by -XX:+PrintFlagsFinal.

Constructor Summary

Constructors

Constructor	Description
CompactObjectHeadersExamples()

Method Summary

Modifier and Type	Method	Description
CompactObjectHeadersExamples.VmFlagState	disabledFlagState()	Reads the compact-object-headers VM flag after disabling it explicitly.
CompactObjectHeadersExamples.VmFlagState	enabledFlagState()	Reads the compact-object-headers VM flag after enabling it explicitly.
String	executableBoundary()	Explains the executable boundary of this example.
String	measurementCaution()	Explains why memory savings are not asserted in the unit test.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

CompactObjectHeadersExamples

public CompactObjectHeadersExamples()

Method Details

enabledFlagState

public CompactObjectHeadersExamples.VmFlagState enabledFlagState()
                                                          throws IOException,
InterruptedException

Reads the compact-object-headers VM flag after enabling it explicitly.

Returns:

the VM-reported flag state

Throws:

IOException - if the child JVM cannot be started

InterruptedException - if interrupted while waiting for the child JVM

disabledFlagState

public CompactObjectHeadersExamples.VmFlagState disabledFlagState()
                                                           throws IOException,
InterruptedException

Reads the compact-object-headers VM flag after disabling it explicitly.

Returns:

the VM-reported flag state

Throws:

IOException - if the child JVM cannot be started

InterruptedException - if interrupted while waiting for the child JVM

executableBoundary

public String executableBoundary()

Explains the executable boundary of this example.

Returns:

a short explanation

measurementCaution

public String measurementCaution()

Explains why memory savings are not asserted in the unit test.

Returns:

a short explanation