JVM内存四大类型：Heap，Stack，Contant，DirectMemory等

Stack属于栈的区域，属于每条线程私有的。

方法区和本地方法栈有很大的不同，方法区是用Java级别角度做的代码，本地方法栈指向的是C/C++。

Java开发，对象就在堆中，一般而言，堆中只有对象。

堆溢出测试：程序运行设置：-verbose:gc -Xms10M -Xmx10M -Xss128k -XX:+PrintGCDetails

package com.dt.spark.jvm.basics;

import java.util.ArrayList;

import java.util.List;

class Person{ }

public class HelloHeapOutOfMemory {

         public static void main(String[] args) {

                   System.out.println("HelloHeapOutOfMemory");

                   List persons = new ArrayList();

                   int counter = 0;

                while(true){

                         persons.add(new Person());

                         System.out.println("Instance: " + (++counter));

                }

         }

}

报错：Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

栈溢出测试:

package com.dt.spark.jvm.basics;

public class  HelloStackOverFlow {

    private int counter;

    public void count() {

       counter++;
 
       count();

    }

    public static void main(String[] args) {

        System.out.println("HelloStackOverFlow");

        HelloStackOverFlow helloStackOverFlow= new HelloStackOverFlow();

        try {

            helloStackOverFlow.count();

        } catch(Exception e) {

            e.printStackTrace();

            throw e;

        }   

    }

}

报错：Exception in thread "main" java.lang.StackOverflowError

常量区溢出报错测试：

package com.dt.spark.jvm.basics;

import java.util.ArrayList;

import java.util.List;

public class HelloConstantOutOfMemory {

         public static void main(String[] args) {

                    try {

                    List stringList = new ArrayList();

                    int item = 0;

                    while(true){

                       stringList.add(String.valueOf(item++).intern());

                    }

                } catch (Exception e) {

                    e.printStackTrace();

                    throw e;

                }

         }

}

报错：Exception in thread "main" [Full GC (Ergonomics) java.lang.OutOfMemoryError: GC overhead limit exceeded

DirectMemory溢出报错测试:

package com.dt.spark.jvm.basics;

import java.nio.ByteBuffer;

public class HelloDirectMemoryOutOfmemory {

    private static final int ONE_GB = 1024*1024*1024;

     private static int count= 1;

    public static void main(String[] args) {

          try {          

               while (true) {

                  ByteBuffer buffer = ByteBuffer.allocateDirect(ONE_GB);

                  count++;
               }

           } catch (Exception e) {

               System.out.println("Exception:instance created "+count);

               e.printStackTrace();

           } catch (Error e) {

               System.out.println("Error:instance created "+count);

               e.printStackTrace();

           }
    }

}

报错：java.lang.OutOfMemoryError: Direct buffer memory