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How to parseInt octets out from an I.P address, store as int variables then return using a presupplied driver method

I'm struggling a bit here. I need to take an I.P address supplied as a string and store as a dotted decimal. split it into its 4 octets that need to be stored as int variables. Which I believe I've done here in its constructor and then using a presupplied driver method return each octet. I can't figure out how to access and send them in the "getOctet" method.
Heres the class file:
public class IpAddress
{
private String dottedDecimal;
private int firstOctet;
private int secondOctet;
private int thirdOctet;
private int fourthOctet;
//**************************************************************
public IpAddress()
{ } // end 0 parameter constructor
//*************************************************
public IpAddress(String d)
{
this.dottedDecimal = d;
String[] ipArr = dottedDecimal.split("\\.");
this.firstOctet = Integer.parseInt(ipArr[0]);
this.secondOctet = Integer.parseInt(ipArr[1]);
this.thirdOctet = Integer.parseInt(ipArr[2]);
this.fourthOctet = Integer.parseInt(ipArr[3]);
} // end 1 parameter constructor
//************************************************************
public String getDottedDecimal()
{
return this.dottedDecimal;
}
//********************************************************
public String getOctet(int n)
{
}
Here is the driver method I have to use unchanged:
public static void main(String[] args)
{
IpAddress ip = new IpAddress("216.27.6.136");
System.out.println(ip.getDottedDecimal());
System.out.println(ip.getOctet(4));
System.out.println(ip.getOctet(1));
System.out.println(ip.getOctet(3));
System.out.println(ip.getOctet(2));
} // end main
Any guidance would be greatly appreciated. I think I have to use an array, which I've tried but I don't exactly know how to use, Arrays are technically the next module we're learning after this assignment so I haven't actually learned how to use them yet

I did this for getOctet method and it seems to work.
It isn't exactly elegant but it worked
public int getOctet(int n)
{
int arr[] = new int[5];
arr[0] = 0;
arr[1]= this.firstOctet;
arr[2]= this.secondOctet;
arr[3]= this.thirdOctet;
arr[4]= this.fourthOctet;
return arr[n];
} // end getOctet

How to make an array from a class defined inside another class

I am a novice Java programmer trying to use classes defined in a different file. So, I've written these two .java files:
First, there's MyLibrary.java:
package mymainprogram;
public class MyLibrary {
public class MyRecord {
int number;
char letter;
}
public static int TriplePlusThree(int input_number) {
return ((input_number*3) + 3);
}
}
Then, MyMainProgram.java:
package mymainprogram;
import java.util.Scanner;
public class MyMainProgram {
public static void main(String[] args) {
Scanner keyread = new Scanner(System.in);
System.out.print("Enter Number to Process: ");
int num = keyread.nextInt();
int result = MyLibrary.TriplePlusThree(num);
System.out.println("3x + 3 = "+result);
String letters = "ABCDEFGHIJ";
MyLibrary.MyRecord[] TenRecs = new MyLibrary.MyRecord[10];
for (int i = 0; i < 10; i++) {
TenRecs[i].number = i; //NullPointerException here
TenRecs[i].letter = letters.charAt(i);
}
}
}
I had no problem getting the method to work just fine; now my goal is to create an array where each member of the array has an integer and character. (Note: I'm not looking for better ways to accomplish this objective; I'm merely using this trivial example to try to get this working).
When I tried to run my program, I got:
java.lang.NullPointerException
I researched this, and found this page, which says:
If we try to access the objects even before creating them, run time errors would occur. For instance, the following statement throws a NullPointerException during runtime which indicates that [this array] isn't yet pointing to [an] object. The objects have to be instantiated using the constructor of the class and their references should be assigned to the array elements in the following way.
studentArray[0] = new Student();
So, I tried to do that in my Main Program:
MyRecordArray[0] = new MyLibrary.MyRecord();
but that gives this error:
an enclosing instance that contains MyLibrary.MyRecord is required
That error message led me to this Stack Exchange question, which says:
you have to create an object of X class (outer class) and then use objX.new InnerClass() syntax to create an object of Y class.
X x = new X();
X.Y y = x.new Y();
So, in accordance with that answer, I've added these two lines to my program:
MyLibrary mylibrary = new MyLibrary();
MyLibrary.MyRecord myrecord = mylibrary.new MyRecord();
Those lines don't give any warnings or compilation errors, so I feel like I'm one step closer, but I'm still trying to figure out how to make an array. I know if I wanted to make an array of integers, I would simply do this:
int[] TenInts = new int[10];
So, I've tried things like:
myrecord[] TenRecs = new myrecord[10];
MyRecord[] TenRecs = new MyRecord[10];
But nothing is working, and I feel like I'm grasping at straws now. I get the feeling that the right set of eyes could solve this pretty quickly.

You need to declare the inner class as static.
You can modify the code as follows to suit your requirements:
This is the code for MyLibrary
public class MyLibrary {
public static class MyRecord{
int number;
char letter;
public MyRecord(){
number = 0;
letter = '\0';
}
public MyRecord(int number, char letter){
this.number = number;
this.letter = letter;
}
}
public static int TriplePlusThree(int input_number){
return (input_number * 3 + 3);
}
}
This is the code for the MyMainProgram
import java.util.Scanner;
public class MyMainProgram {
public static void main(String[] args){
Scanner in = new Scanner(System.in);
System.out.println("Enter number to process");
int num = in.nextInt();
System.out.println("3x + 3 = " + MyLibrary.TriplePlusThree(num));
String letters = "ABCDEFGHIJ";
MyLibrary.MyRecord[] TenRecords = new MyLibrary.MyRecord[2];
for (int i=0; i<TenRecords.length; i++){
TenRecords[i] = new MyLibrary.MyRecord();
TenRecords[i].number = i;
TenRecords[i].letter = letters.charAt(i);
}
// Printing class records
for (int i=0; i<TenRecords.length; i++){
System.out.println("Printing records of record " + i + " : ");
System.out.println("Number : " + TenRecords[i].number);
System.out.println("Letter : " + TenRecords[i].letter);
}
in.close();
}
}
You can create the instance of the inner class as follows:
TenRecords[i] = new MyLibrary.MyRecord();
Hope this helps.

The nested class MyRecord contains a hidden reference to the outer class MyLibrary and therefore must be associated with an instance of MyLibrary. This way MyRecord can access private members of MyLibrary.
MyLibrary.MyRecord myrecord = mylibrary.new MyRecord();
Wow, this is funny syntax. In all my years of java programming, I never used such a construct. Typically, you would create objects of inner classes (MyRecord) within the outer class (MyLibrary). Another common thing is to declare the inner class as static which would eliminate the need for an instance of the outer class.
MyRecord[] TenRecs = new MyRecord[10];
This will create an array where all the elements are NULL. You have to initialize each of them (e.g. with a loop).

If you initialize MyRecord[10] the array has null objects. You still have to initialize each element in the array to a new MyRecord object. Otherwise you will get the NPE.
one way to do is : List<MyRecord> TenRecs = new ArrayList<MyRecord>();
TenRecs.add( new MyRecord() );
or for ( int i = 0; i < 10; i++ ) TenRecs[i] = new MyRecord();
also if you add an import statement : import mymainpackage.MyLibrary.MyRecord; You don't need to do mylibrary.new MyRecord(); just do new MyRecord();

You have to create each object in array before initialize. Refer to this link.
Create each object like this.
MyLibrary outer = new MyLibrary();
TenRecs[i] = outer.new MyRecord();
Full code:
MyLibrary.MyRecord[] TenRecs = new MyLibrary.MyRecord[10];
for (int i = 0; i < 10; i++) {
MyLibrary outer = new MyLibrary();
TenRecs[i] = outer.new MyRecord();
TenRecs[i].number = i;
TenRecs[i].letter = letters.charAt(i);
}

There are several points you need to note.
First, difference between a instance inner class and a static inner class.
An instance inner class, declared without static modifier,
public class OutterClass {
public class InstanceInnerClass {}
}
should be created like this:
OutterClass outter = new OutterClass();
InstanceInnerClass iInner = outter.new InstanceInnerClass();
while a static inner class, declared with static modifier,
public class OutterClass {
public static class StaticInnerClass {}
}
should be created like this:
StaticInnerClass sInner = new OutterClass.StaticInnerClass();
Secondly, you accessed an array entry before it is filled
MyLibrary library = new MyLibrary();
MyLibrary.MyRecord[] TenRecs = new MyLibrary.MyRecord[10];
for (int i = 0; i < 10; i++) {
// Create new instance
TenRecs[i] = library.new MyRecord();
TenRecs[i].number = i;
TenRecs[i].letter = letters.charAt(i);
}

How do I get the constructor of a variable?

I am trying to get the constructor of a variable by using an ASTVisitor.
public boolean visit(VariableDeclarationFragment node)
{
IVariableBinding variableBinding = node.resolveBinding();
// I can't seem to get the constructor here
}
SAMPLE
Base b = new Derived(); // How do I get packageNAME.Derived?
int x = 5; // How do I get 5?

You need to look deeper into the syntax tree to find the answers. The ASTView is a great help in cases like this. This is the update site I use with Kepler: http://www.eclipse.org/jdt/ui/update-site
Your Samples could be answered like this (simplyfied):
/*
* Base b = new Derived(); // How do I get packageNAME.Derived?
*/
private String getClassNameFromConstructor(VariableDeclarationFragment fragment) {
Expression initializer = fragment.getInitializer();
if (initializer instanceof ClassInstanceCreation) {
ClassInstanceCreation instanceCreation = (ClassInstanceCreation)initializer;
if (instanceCreation.getType() instanceof SimpleType) {
SimpleType simpleType = (SimpleType)instanceCreation.getType();
return simpleType.getName().getFullyQualifiedName();
}
}
return null;
}
/*
* int x = 5; // How do I get 5?
*/
private String getInitialisationNumber(VariableDeclarationFragment fragment) {
Expression initializer = fragment.getInitializer();
if (initializer instanceof NumberLiteral) {
NumberLiteral numberLiteral = (NumberLiteral)initializer;
return numberLiteral.getToken();
}
return null;
}

Variables don't have constructors. Objects have constructors. Find the assignment, find the expression being assigned, and if that expression is a constructor you can get the class name from that.

Interesting issue about java and linking "&"

I know that there isn't way to access to the links of variables in java (like in &C or &php). But for example I have such task:
public class JustTest {
private int n = 1;
private int x = 10;
public int[] getIntegers() {
return new int[] { n, x };
}
public void filledInteger() {
int[] vals = getIntegers();
System.out.println("Before change");
System.out.println(Arrays.toString(vals));
vals[0] = 2;
vals[1] = 20;
System.out.println("After change");
System.out.println(Arrays.toString(vals));
System.out.println("Values of name & xml");
System.out.println(n);
System.out.println(x);
System.out.println("calling getIntegers");
System.out.println(Arrays.toString(getIntegers()));
}
public static void main(String[] args) {
JustTest t = new JustTest();
t.filledInteger();
}
}
The result is:
Before change
[1, 10]
After change
[2, 20]
Values of name & xml
1
10
calling getIntegers
[1, 10]
So, I want to change values of "n" and "x" fields of the class instance. I can't do this by setting straightly (this->n = 20;), because I may dont know what fields do I have. Only method getIntegers knows.
(No in this code, but for example I have child class with its own fields and in the parent class I have a method filledInteger() which should change specified properties of the child class ( he knows about this properties from the method getIntegers which is abstract in the parent class and implemented in the child class))
Here is simple implementation (without inheritance), using links in php
<?php
class JustTest {
private $n = 1;
private $x = 10;
public function getIntegers() {
return array( &$this->n, &$this->x );
}
public function filledInteger() {
$vals = $this->getIntegers();
echo("Before change" . "<br/>");
echo(print_r($vals, true) . "<br/>");
$vals[0] = 2;
$vals[1] = 20;
echo("After change" . "<br/>");
echo(print_r($vals, true) . "<br/>");
echo("Values of n & x". "<br/>");
echo $this->n , "<br/>";
echo $this->x , "<br/>";
echo("call getIntegers again" . "<br/>");
echo(print_r($this->getIntegers(), true) . "<br/>");
}
}
$t = new JustTest();
$t->filledInteger();
?>
The result is:
Before change
Array ( [0] => 1 [1] => 10 )
After change
Array ( [0] => 2 [1] => 20 )
Values of n & x
2
20
call getIntegers again
Array ( [0] => 2 [1] => 20 )
That is what I exactly need. Im just curious how do I implement this in java
Hope you understood.
Next example:
public abstract class ParentTest {
abstract int[] getIntegers();
public void fillIntegers(int[] newIntegers) {
int[] integersOfChild = getIntegers();
for (int i = 0; i < integersOfChild.length; i++) {
integersOfChild[i] = newIntegers[i];
}
}
}
public class ChildTest extends ParentTest {
private int x;
private int y;
#Override
int[] getIntegers() {
return new int[] {x, y};
}
}
public class UseTest {
void main() {
List<ParentTest> list;
for (ParentTest item : list) {
item.fillIntegers(myItegers);
}
}
}
This is what I need. I have a list of ParentTest instances (it may be ChildTest, or ChildTest2, or ChildTest3; but they all children of a ParentTest) and I need to fill all fields with my integer values, but I dont know if items in the list instances of a ChildTest, or ChildTest2, or ChildTest3 class

How do I implement this in Java?
With great pain via the Reflection API. If you want to write code like this, the best idea is to use another language.
Consider programming in Groovy instead. You can use array syntax to directly access class members by name: t["n"] = 2; This works with legacy Java code, so there is no need to modify TestClass to support this usage.

The concept you are talking about is called pass by reference. Java has for the most part abandoned it - it creates too many side-effects, like the one you are seeing here.
The issue is that while unfortunately you can't do this here, it actually prevents a huge number of unintentional bugs being released.

What about something like that:
public final class JustTest {
private final Map<String, Object> fields;
public void filledInteger() {
System.out.println("Before change\n" + this.fields);
fields.put("N", 2);
fields.put("X", 20);
System.out.println("After change\n" + this.fields);
System.out.println("Values of name & xml\n" + fields.get("N")
+ "\n" + fields.get("X"));
}
private JustTest() {
this.fields = Maps.newHashMap(); // guava
fields.put("N", 1);
fields.put("X", 10);
}
public static void main(String[] args) {
final JustTest t = new JustTest();
t.filledInteger();
}
}

You can't do individual fields without reflection, but you can change the contents of collections. Note that this is not really intended behavior, but rather something you have to be careful of when using collections.
This outputs 5 3 2 4 2 4
public class Test
{
public Vector<Integer> args = new Vector<Integer>();
public void fillArgs()
{
args.add(5);
args.add(3);
}
public Vector<Integer> getArgs()
{
return args;
}
public static void main(String args[])
{
Test s = new Test();
s.fillArgs();
Vector<Integer> temp = s.getArgs();
for (Integer i : temp)
System.out.println(i);
temp.setElementAt(2, 0);
temp.setElementAt(4, 1);
for (Integer i : temp)
System.out.println(i);
for (Integer i : s.getArgs())
System.out.println(i);
}
}

Your php example does not return an array of ints, but rather an array of int pointers. This is NOT something you can do in Java, in fact, this is NOT something you want to do in Java. Give a use case, and there is likely a better way to solve the problem you have.
If you want to return an object that others can affect and that are contained as member variables, do that. An ArrayList, HashMap, etc... there are plenty of things that can fit your needs. If you are given someone elses class and you must stick your nose in their code, you can get around their private declaration doing the following:
public void setN(JustTest j, int n) {
//You would handle some exceptions here also
Field f = JustTest.class.getDeclaredField("n");
f.setInt(j, n);
}

Javolution ByteBuffer question

I have the following implementation with Javolution:
public class RunScan extends Struct
{
public final Signed32 numOfClusters = new Signed32();
public final ClusterData[] clusters;
public final Signed32 numOfRecons = new Signed32();
public final ReconData[] recons ;
public RunScan (int numOfClusters, int numOfRecons)
{
this.numOfClusters.set(numOfClusters);
this.numOfRecons.set(numOfRecons);
clusters = array(new ClusterData[numOfClusters]);
recons = array(new ReconData[numOfRecons]);
}
}
public class ClusterData extends Struct
{
public final UTF8String scanType = new UTF8String(CommInterfaceFieldConstants.SCAN_TYPE_SIZE);
public final UTF8String patientId = new UTF8String(CommInterfaceFieldConstants.PATIENT_ID_SIZE);
.
.
.
}
public class ReconData extends Struct
{
public final UTF8String patientId = new UTF8String(CommInterfaceFieldConstants.PATIENT_ID_SIZE);
public final UTF8String scanSeriesId = new UTF8String(CommInterfaceFieldConstants.SCAN_SERIES_ID_SIZE);
.
.
.
}
In our communication class, before we put data onto socket, we need to get the bytes[] of the RunScan object but we get BufferUnderflowException in the line with "//<<<<<<<":
private byte[] getCmdBytes(Struct scCmd)
{
ByteBuffer cmdBuffer = scCmd.getByteBuffer();
int cmdSize = scCmd.size();
byte[] cmdBytes = new byte[cmdSize];
if (cmdBuffer.hasArray())
{
int offset = cmdBuffer.arrayOffset() + scCmd.getByteBufferPosition();
System.arraycopy(cmdBuffer.array(), offset, cmdBytes, 0, cmdSize);
}
else
{
String msg = "\n\ncmdBufferRemaining=" + cmdBuffer.remaining() + ", cmdBytesSize=" + cmdBytes.length + "\n\n";
System.out.println(msg);
cmdBuffer.position(scCmd.getByteBufferPosition());
cmdBuffer.get(cmdBytes); //<<<<<<<<<< underFlowException
}
return cmdBytes;
}
This method works in other cases. The exception happens because this line,
ByteBuffer cmdBuffer = scCmd.getByteBuffer();
only returns a 8 bytes (from the remaining() method) ByteBuffer of the RunScan object which are those two Signed32 fields, I think. But this line,
int cmdSize = scCmd.size();
returns a right length of the RunScan object which includes the size of those two arrays.
If I create those two array at the time I declare them (not "new" them in the constructor) with hard coded length, it works fine without any exception.
Anybody can help me figure out what's wrong with our implementation?

I ran into a similar situation with my code. Generally, with the current Struct object, you cannot have a variable length array defined in the same struct as the member that contains the number of elements in the array.
Try something like this:
public class RunScanHeader extends Struct
{
public final Signed32 numOfClusters = new Signed32();
public final Signed32 numOfRecons = new Signed32();
}
public class RunScanBody extends Struct
{
public final ClusterData[] clusters;
public final ReconData[] recons ;
public RunScan (int numOfClusters, int numOfRecons)
{
clusters = array(new ClusterData[numOfClusters]);
recons = array(new ReconData[numOfRecons]);
}
}
You'll then need a two phase approach to read and write, first read/write the header data, then read/write the body data.
Sorry I don't have more details at this time, if you can't solve this, let me know and I'll dig back through my code.

The initialization order is important has it defines the position of each field. Either your initialization is done when the field is declared (most common case). Or if you do it in the constructor you have to remember that the constructor is called after the member initialization. Here is an example with initialization done in the constructor:
public class RunScan extends Struct {
public final Signed32 numOfClusters;
public final ClusterData[] clusters;
public final Signed32 numOfRecons;
public final ReconData[] recons ;
public RunScan (int numOfClusters, int numOfRecons) {
// Initialization done in the constructor for all members
// Order is important, it should match the declarative order to ensure proper positioning.
this.numOfClusters = new Signed32();
this.clusters = array(new ClusterData[numOfClusters]);
this.numOfRecons = new Signed32();
this.recons = array(new ReconData[numOfRecons]);
// Only after all the members have been initialized the set method can be used.
this.numOfClusters.set(numOfClusters);
this.numOfRecons.set(numOfRecons);
}
}

get() will move the position of the ByteBuffer.
scCmd.getByteBuffer().slice().get(dest) might solve your issue with moving the position and unintended side effects.
scCmd.getByteBuffer().duplicate().get(dest) might also solve your issue if slice() produces the wrong picture of the origin buffer.
Additionally, it appears as though scCmd.getByteBuffer() creates a redundant reference and you are calling the source and child reference in the same method.
If scCmd.getByteBuffer() is already passing you a slice(), your redundant access to these methods is certainly going to do something other than what you planned.