how to get the jvm default heap size

C:\bea1033\jdk160_18\bin>.\java -XX:+PrintCommandLineFlags -version

-XX:InitialHeapSize=16777216 -XX:MaxHeapSize=268435456 -XX:+PrintCommandLineFlags -XX:-UseLargePagesIndividualAllocation

java version "1.6.0_18"

Java(TM) SE Runtime Environment (build 1.6.0_18-b07)

Java HotSpot(TM) Client VM (build 16.0-b13, mixed mode)

C:\bea1033\jdk160_18\bin>.\java -Xmx1024m -XX:+PrintCommandLineFlags -version

-XX:InitialHeapSize=16777216 -XX:MaxHeapSize=1073741824 -XX:+PrintCommandLineFlags -XX:-UseLargePagesIndividualAllocation

java version "1.6.0_18"

Java(TM) SE Runtime Environment (build 1.6.0_18-b07)

Java HotSpot(TM) Client VM (build 16.0-b13, mixed mode)

C:\bea1033\jdk160_18\bin>cd C:\jdk1.5.0_22\bin

C:\jdk1.5.0_22\bin>java a

************************

2031616

1

************************

66650112

63

************************

C:\jdk1.5.0_22\bin>cd C:\bea1033\jdk160_18\bin

C:\bea1033\jdk160_18\bin>.\java -Xmx1024m -XX:+PrintCommandLineFlags -version >aa.log

java version "1.6.0_18"

Java(TM) SE Runtime Environment (build 1.6.0_18-b07)

Java HotSpot(TM) Client VM (build 16.0-b13, mixed mode)

C:\bea1033\jdk160_18\bin>java -XX:+PrintFlagsFinal -version

Unrecognized VM option '+PrintFlagsFinal'

Could not create the Java virtual machine.

C:\bea1033\jdk160_18\bin>.\java -server -Xmx1024m -XX:+PrintCommandLineFlags -version

-XX:InitialHeapSize=50129664 -XX:MaxHeapSize=1073741824 -XX:ParallelGCThreads=4 -XX:+PrintCommandLineFlags -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

java version "1.6.0_18"

Java(TM) SE Runtime Environment (build 1.6.0_18-b07)

Java HotSpot(TM) Server VM (build 16.0-b13, mixed mode)

C:\bea1033\jdk160_18\bin>.\java -server  -XX:+PrintCommandLineFlags -version

-XX:InitialHeapSize=50129664 -XX:MaxHeapSize=802074624 -XX:ParallelGCThreads=4 -XX:+PrintCommandLineFlags -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

java version "1.6.0_18"

Java(TM) SE Runtime Environment (build 1.6.0_18-b07)

Java HotSpot(TM) Server VM (build 16.0-b13, mixed mode)

C:\bea1033\jdk160_18\bin>java a

************************

16252928

15

************************

259522560

247

************************

C:\bea1033\jdk160_18\bin>java -server a

************************

48103424

45

************************

714014720

680

************************

C:\bea1033\jdk160_18\bin>java -client a

************************

16252928

15

************************

259522560

247

************************

C:\bea1033\jdk160_18\bin>cd C:\jdk1.5.0_22\bin

C:\jdk1.5.0_22\bin>java -client a

************************

2031616

1

************************

66650112

63

************************

C:\jdk1.5.0_22\bin>java -server a

************************

33554432

32

************************

517013504

493

************************

C:\jdk1.5.0_22\bin>

 

 

 1. 用 -client -server default不同

 2.  1.5 与1.6又不同

 3.程序得到的结果与实际不相同？？

 

C:\jdk1.5.0_22\bin\a.java

 

public class a  {

public static void main(String[] a){

 System.out.println("************************");

    System.out.println(Runtime.getRuntime().totalMemory());

  System.out.println(Runtime.getRuntime().totalMemory()/1024/1024);

 

   System.out.println("************************");

 

   System.out.println(Runtime.getRuntime().maxMemory());

  System.out.println(Runtime.getRuntime().maxMemory()/1024/1024);

  System.out.println("************************");

}

}