javademos/lanes/src/UnsafeWarning.java

import java.lang.reflect.Field;
import sun.misc.Unsafe;

/**
 * "sun.misc.Unsafe memory methods deprecated for removal": JEP 471 (23) deprecated them, JEP 498 (24) makes the first
 * call print a warning at run time. This allocates and frees 8 bytes off-heap and shows what the JVM says.
 * Chapter: docs/14-lanes-21-to-25.md
 */
public class UnsafeWarning {
    @SuppressWarnings("removal")
    public static void main(String[] args) throws Exception {
        System.out.println("java.version = " + System.getProperty("java.version"));
        Field f = Unsafe.class.getDeclaredField("theUnsafe");
        f.setAccessible(true);
        Unsafe u = (Unsafe) f.get(null);
        long addr = u.allocateMemory(8);
        u.putLong(addr, 42L);
        System.out.println("read back: " + u.getLong(addr));
        u.freeMemory(addr);
    }
}