JVM学习分享-练习题

package org.fenixsoft.clazz;

public class TestClass {
    private int m;

    public int inc() {
        return m + 1;
    }
}

//----------- javap -verbose TestClass

package zero.desk.metaspace;

import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;

/**
 * @author:Zero
 * @Description:
 * @since 2019/6/11.
 * 练习1
 * VM Options：-XX:MetaspaceSize=10M -XX:MaxMetaspaceSize=10M
 */
public class MetaspaceOutmemory {
    public static void main(String[] args) {
        try {
            System.out.println("MetaspaceOOM.java");
            while (true) {
                Enhancer enhancer = new Enhancer();
                enhancer.setSuperclass(OOMObject.class);
                enhancer.setUseCache(false);
                enhancer.setCallback(
                        (MethodInterceptor) (obj, method, args1, methodProxy) -> methodProxy.invokeSuper(obj, args1)
                );
                enhancer.create();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    static class OOMObject {
    }
}

//------------------

package zero.desk.metaspace;

import java.util.ArrayList;
import java.util.List;

/**
 * @author:Zero
 * @Description:
 * @since 2019/6/11.
 * 练习2
 * VM Options：-Xmx1M -Xms1M
 */
public class StringOutmemory {
    static String base = "string";

    public static void main(String[] args) {
        try {
            Thread.sleep(1000);
            List<String> list = new ArrayList<String>();
            for (int i = 0; i < Integer.MAX_VALUE; i++) {
                String str = base + base;
                base = str;
                list.add(str.intern());
            }
        }catch (Exception e) {
            e.printStackTrace();
        }

    }
}

//-------------

package zero.desk.gc;

/**
 * @author Zero
 * @since 2019-09-08.
 * Description:使用默认垃圾收集器，Parallel Scavenge + Parallel Old
 * 练习3
 * VM Options：-XX:+PrintGCTimeStamps -XX:+PrintGCDateStamps -XX:+PrintGCDetails
 */
public class ReferenceCountingGC {
    public Object instance = null;
    private static final int ONE_MB = 1024 * 1024;

    private byte[] bigSize = new byte[2 * ONE_MB];

    public static void main(String[] args) throws InterruptedException {
        Thread.sleep(1000);
        testGC();
        Thread.sleep(1000);
    }

    public static void testGC() {
        ReferenceCountingGC objA = new ReferenceCountingGC();
        ReferenceCountingGC objB = new ReferenceCountingGC();
        objA.instance = objB;
        objB.instance = objA;

        objA = null;
        objB = null;

        System.gc();
    }
}

//-------------

package zero.desk.gc;

/**
 * @author Zero
 * @since 2019-09-08.
 * Description:使用CMS收集器，ParNew  + CMS
 * 练习4
 * VM Options：-XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:+CMSParallelRemarkEnabled -XX:+UseCMSCompactAtFullCollection -XX:+PrintClassHistogram -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC
 */
public class ReferenceCountingGCOpen {
    public Object instance = null;
    private static final int ONE_MB = 1024 * 1024;

    private byte[] bigSize = new byte[2 * ONE_MB];

    public static void main(String[] args) throws InterruptedException {
        Thread.sleep(2000);
        testGC();
        Thread.sleep(1000);
    }

    public static void testGC() {
        ReferenceCountingGCOpen objA = new ReferenceCountingGCOpen();
        ReferenceCountingGCOpen objB = new ReferenceCountingGCOpen();
        objA.instance = objB;
        objB.instance = objA;

        objA = null;
        objB = null;

        System.gc();
    }
}

//--------------

package zero.desk.constantpool;

/**
 * @author Zero
 * @since 2019-09-08.
 * Description:
 * 练习5
 * javap -verbose ConstantPool
 */
public class ConstantPool extends C implements A,B{
    private String str = "test string";
    private final int a = 10;
    private final long b = 10;
    private final long bb = 100;
    private int c = 11;
    private float d = 12f;
    private float e = 12f;
    private double ee = 12f;

    private int m;

    public int inc() {
        return m + 1;
    }
}