Java Memory

Some good references to understand java memory problems.

Read BEST practices to avoid memory leaks

http://jb2works.com/memoryleak/topfive.html

Memory leaks with tools to diagonise :

http://jb2works.com/memoryleak/index.html

Java Memory Puzzle Eye Opener

http://mattfleming.com/node/306


My Memory Related Experiments :

Experiment 1 :

Enviornment : Processor=2.80 Memory=1.93GB(2072321024 bytes) RAM

Case 1 : I ran a program and printed memory using Runtime.getRuntime().maxMemory() Output : 66650112 bytes OR 63.5625 MB

Case 2 : Then i passed argument -Xmx512m and printed memory Runtime.getRuntime().maxMemory()
Output : 532742144 bytes OR 508.0625 MB

Case 3 : Then i passed argument -Xmx1200m and printed memory Runtime.getRuntime().maxMemory()
Output : 1248657408 bytes OR 1190.8125 MB OR 1.16GB

Case 4 : Then i passed argument -Xmx1612m and printed memory Runtime.getRuntime().maxMemory()
Output : 1677328384 bytes OR 1599.625 MB OR 1.56GB

But when i tried to give 1613 or more it started giving error :
Error occurred during initialization of VM Could not reserve enough space for object heap

Experiment 2 :

Case 1 :

public class Test {

public static void ppp1() {
byte[] test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
}
public static void ppp2() {
byte[] test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
}
public static void main(String args[]) {
ppp1();
ppp2();
}
}

O/P : Works Properly

Case 2 :

public class Test {

public static void ppp1() {
byte[] test1 = null;
byte[] test2 = null;
try {
test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
   e.printStackTrace();
}
try {
test2 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
    e.printStackTrace();
}
}

public static void main(String args[]) {
ppp1();
}
}

O/P : Gives Out of Memory

Case 3 :

public class Test {

public static void ppp1() {
byte[] test1 = null;
byte[] test2 = null;
try {
test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
   e.printStackTrace();
}
test1 = null;
try {
test2 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
    e.printStackTrace();
}
}

public static void main(String args[]) {
ppp1();
}
}

O/P : Works Properly

Case 4 :

public class Test {

public static void ppp1() {
byte[] test1 = null;
byte[] test2 = null;
byte[] test3 = null;
try {
test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
test3 = test1;
} catch(Exception e) {
   e.printStackTrace();
}
test1 = null;
try {
test2 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
    e.printStackTrace();
}
}

public static void main(String args[]) {
ppp1();
}
}

O/P : Gives Out of Memory

Case 5 :

public class Test {

public static void ppp1() {
byte[] test1 = null;
byte[] test2 = null;
byte[] test3 = null;
try {
test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
test3 = test1;
} catch(Exception e) {
   e.printStackTrace();
}
test1 = null;
  test3 = null;
try {
test2 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
    e.printStackTrace();
}
}

public static void main(String args[]) {
ppp1();
}
}

O/P : Works Properly


Experiment 3 :

Case 1 :

public class Test {

public static void ppp1() {
byte[] test1 = null;
byte[] test2 = null;
try {
test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
   e.printStackTrace();
}
try {
test2 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
    e.printStackTrace();
}
}

public static void main(String args[]) {
ppp1();
}
}


O/P :  Gives Out of Memory

Case 2 :

public class Test {

public static void ppp1() {
byte[] test1 = null;
byte[] test2 = null;
try {
test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
   e.printStackTrace();
}
for(int i=0; i< 100000; i++) {
   
  }
try {
test2 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
    e.printStackTrace();
}
}

public static void main(String args[]) {
ppp1();
}
}

O/P : Works Properly. For index condition i less than 100000 it was giving Out of memory.

Case 3 :

public class Test {

public static void ppp1() {
try {
byte[] test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
   e.printStackTrace();
}
try {
byte[] test2 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
    e.printStackTrace();
}
}

public static void main(String args[]) {
ppp1();
}
}

O/P :  Gives Out of Memory

Case 4 :

public class Test {

public static void ppp1() {
try {
byte[] test1 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
   e.printStackTrace();
}
for(int i=0; i < 0; i++) {
   
  }
try {
byte[] test2 = new byte[(int)(Runtime.getRuntime().maxMemory()/2)];
} catch(Exception e) {
    e.printStackTrace();
}
}

public static void main(String args[]) {
ppp1();
}
}

O/P : Works Properly for any condition i less than 0, 1, 2 .. it was working.