Creating a generic class with a constructor that takes an array of objects

I am relatively new to java and want to build a quick utility class that can generate a Run Length Encoding of any object. The idea is to take an array of objects of type "O" and then encode a string of objects that are "equal" to each other as an integer that counts the number of such equal instances and a single copy of the instance. This has the potential to very quickly reduce the size of some objects that I want to store. I would like to implement this class as a generic.
public class RunLengthEncoding<O> {
     private class RLEPair {
          private int length;
          private O object;
     public RunLengthEncoding(O[]) {
}As you can see, I need to make a constructor that takes an array of type "O". Is this possible to do? I can't seem to find the right syntax for it.
Thanks,
Sean

Sorry. Obvious answer:
public RunLengthEncoding(O[] oarray) {Again, sorry for the noise.

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Why can't classes with private constructors be subclassed?

Why can't classes with private constructors be subclassed?
I know specifying a private nullary constructor means you dont want the class to be instantiated or the class is a factory or a singleton pattern. I know the workaround is to just wrap all the methods of the intended superclass, but that just seems less wizardly.
Example:
I really, really want to be able to subclass java.util.Arrays, like so:
package com.tassajara.util;
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        for (int i = 0; i < array.length; i++)
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List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Character(array[i]));
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public static List asList( byte[] array) {
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List result = new LinkedList();
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for (int i = 0; i < array.length; i++)
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// Now that we extend java.util.Arrays this method is not needed.
// /**JCF already does this so just wrap their implementation
// public static List asList(Object[] array) {
// return java.util.Arrays.asList(array);
public static List asList(Object object) {
List result;
Class type = object.getClass().getComponentType();
if (type != null && type.isPrimitive()) {
if (type == Boolean.TYPE)
result = asList((boolean[])object);
else if (type == Character.TYPE)
result = asList(( char[])object);
else if (type == Byte.TYPE)
result = asList(( byte[])object);
else if (type == Short.TYPE)
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I do not intend to instantiate com.tassajara.util.Arrays as all my methods are static just like java.util.Arrays. You can see where I started to wrap asList(Object[] o). I could continue and wrap all of java.util.Arrays methods, but thats annoying and much less elegant.

Why can't classes with private constructors be
subclassed?Because the subclass can't access the superclass constructor.
I really, really want to be able to subclass
java.util.Arrays, like so:Why? It only contains static methods, so why don't you just create a separate class?
I do not intend to instantiate
com.tassajara.util.Arrays as all my methods are static
just like java.util.Arrays. You can see where I
started to wrap asList(Object[] o). I could continue
and wrap all of java.util.Arrays methods, but thats
annoying and much less elegant.There's no need to duplicate all the methods - just call them when you want to use them.
It really does sound like you're barking up the wrong tree here. I can see no good reason to want to subclass java.util.Arrays. Could you could explain why you want to do that? - perhaps you are misunderstanding static methods.
Precisely as you said, if they didn't want me to
subclass it they would have declared it final.Classes with no non-private constructors are implicitly final.
But they didn't. There has to be a way for an API
developer to indicate that a class is merely not to be
instantiated, and not both uninstantiable and
unextendable.There is - declare it abstract. Since that isn't what was done here, I would assume the writers don't want you to be able to subclass java.util.Arrays

Re: How to create More two class with one object

haii,
         i have small information How to create More two class with one object,
bye
bye
babu

Hello
I assume you want to create multiple instance of your class.
Assuming that you class is NOT a singleton then simply repeat the CREATE OBJECT statement as many times as you need.
TYPES: begin of ty_s_class.
TYPES: instance   TYPE REF TO zcl_myclass.
TYPES: end of ty_s_class.
DATA:
lt_itab      TYPE STANDARD TABLE OF ty_s_class
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ls_record TYPE ty_s_class.
DO 10 TIMES.
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ENDDO.
Regards
Uwe

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Problem in creating a generic datasource with infoset

Dear Expert,
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Constructor that takes Comparator parameter

Hello,
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MindGames wrote:
Hello,
How would you implement a new Constructor for a class that takes a Comparator<> parameter?The same way, you'd implement a new Constructor that takes any other parameter.
What's the problem? Where are you stuck?

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Default class with public constructor - why?

Noticed some code that had a class with package-level access and a public constructor - wondered what the benefit/use of that would be... Thanks!

GarudaJava wrote:
Noticed some code that had a class with package-level access and a public constructor - wondered what the benefit/use of that would be... Thanks!If the class itself doesn't need to be exposed, but it implements some interface, and is assumed to have a public no-arg consturctor, it could be created reflexively. This is a contrived situation, but it's the only one I can think of in Java where that'd be useful.
package foo;
class Foo implements SomeInterface {
public Foo() {
package factory;
class Factory {
public static SomeInterface create(Class<? extends SomeInterface> clazz) { // not sure if I got the generics right, but they're incidendtal to the example
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package foo;
import factory.Factory;
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public void bar() {
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}Like I said, pretty contrived, and I can't think of a real-world use case that matches it offhand, but structurally it'd look something like that.
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Need help with generic class with comparable type

Hi. I'm at University, and I have some coursework to do on writing a generic class which offers ordered binary trees of items which implement the comparable interface.
I cant get the code to compile which I have written.
I get the error: OBTComparable.java uses unchecked or unsafe operations
this is the more detailed information of the error when I compile with -Xlint:unchecked
OBTComparable.java:62: warning: [unchecked] unchecked call to insert(OBTType) as
a member of the raw type OBTComparable
left.insert(insertValue);
^
OBTComparable.java:64: warning: [unchecked] unchecked call to insert(OBTType) as
a member of the raw type OBTComparable
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^
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public class OBTComparable<OBTType extends Comparable<OBTType>>
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private boolean empty;
// If the tree is not empty then it has
// a value, a left and a right.
// These are not used it empty == true
private OBTType value;
private OBTComparable left;
private OBTComparable right;
// Create an empty tree.
public OBTComparable()
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} // OBTComparable
// Make this tree into an empty tree.
private void setEmpty()
    empty = true;
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    left = null;
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} // setEmpty
// See if this is an empty (Sub)tree.
public boolean isEmpty()
{ return empty; }
// Get the value which is here.
public OBTType getValue()
{ return value; }
// Get the left sub-tree.
public OBTComparable getLeft()
{ return left; }
// Get the right sub-tree.
public OBTComparable getRight()
{ return right; }
// Store a value at this position in the tree.
private void setValue(OBTType requiredValue)
    if (empty)
      empty = false;
      left = new OBTComparable<OBTType>(); // Makes a new empty tree.
      right = new OBTComparable<OBTType>(); // Makes a new empty tree.
    } // if
    value = requiredValue;
} // setValue
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public void insert(OBTType insertValue)
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    else
      right.insert(insertValue);
} // insert
// Find a value
public boolean find(OBTType findValue)
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    else if (findValue.compareTo(value) < 0)
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    else
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} // find
} // OBTComparableI am unsure how to check the types of OBTType I am comparing, I know this is the error. It is the insert method and the find method that are causing it not to compile, as they require comparing one value to another. How to I put the check in the program to see if these two are of the same type so they can be compared?
If anyone can help me with my problem that would be great!
Sorry for the long post, I just wanted to put in all the information I know to make it easier for people to answer.
Thanks in advance
David

I have good news and undecided news.
First the good news. Your code has compiled. Those are warnings not errors. A warning is the compiler's way of saying "I understand what you are asking but maybe you didn't fully think through the consequences and I just thought I would let you know that...[something] "
In this case it's warning you that you aren't using generics. But like I said this isn't stopping it from compiling.
The undecided news is the complier is warning you about not using generics. Are you supposed to use generics for this assignment. My gut says no and if that's true then you have no problem. If you are supposed to use generics well then you have some more work.

Generic classes with parameterized super class and interface

Hello.
I'm trying to write a generic class that looks like the following pseudo-code.
public interface Interface {
    public Interface getSibling(...);
public class Klass {...}
public class MyKlass<T extends Klass, T2 extends Interface>
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}where Interface and Klass each have various extensions.
I came across this problem, or challenge, while writing classes for testing my EJBs. I tried and failed various attempts.
Is it possible to write generic classes of this nature in Java?
If so, please tell me and others who are like me.
Thanks in advance.

No. That would not work.
Beside being forbidden by the compiler, to my understanding, it cannot be done in theory either, as the parameterized types get bound at instantiation time and are not available for static reference, which both extends and implements require.

Class with private constructor can be extended or not

Hi All,
I have a doubt.
if a class has private constructor and there are some methods in this class.Can this class be extended and if yes how can we call its method in subclass?
Thanks
Sumit

Karanjit wrote:
If a class contains only private constructors, then it cannot be extended.Err... not the whole story!
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Problem with string constructor when using byte array as parameter

I am creating a string using constructor and passing byte array as parameter.This byte array i am getting from MessageDigest's digest() method,i.e. a hash value.
The problem is when i iterate through byte array i can able to print all the values in byte array.But when i construct a string from that byte array and printing that string ,that is printing some unknown characters.
I don't know whether i need to pass charsequence to the constructor and the type of charsequence.Can anybody help me?
Thanks in advance

Is there some problem today? I'm getting this sort of thing all over.
I already told you and so did Kayaman. Don't. String is not a holder for binary data. You have to Base-64 encode it. If you don't you cannot reconstruct the original binary digest value, so putting it into a database is completely utterly and entirely pointless.
Is that clear enough?

Help with a store function that takes string array

Hi All,
I have a function that takes in two string arrays, status_array, and gender_array. You can see the partial code below. Somehow if the value for the string array is null, the code doesn't execute properly. It should return all employees, but instead it returns nothing. Any thoughts? THANKS.
for iii in 1 .. status_array.count loop
v_a_list := v_a_list || '''' || status_array(iii) || ''',';
end loop;
v_a_list := substr(v_a_list, 1, length(trim(v_a_list)) - 1);
for iii in 1 .. gender_array.count loop
v_b_list := v_b_list || '''' || gender_array(iii) || ''',';
end loop;
v_b_list := substr(v_b_list, 1, length(trim(v_b_list)) - 1);
IF v_a_list IS NOT NULL and v_b_list IS NOT NULL THEN
v_sql_stmt := 'select distinct full_name from t_employee where status in (' || v_a_list || ') and gender in (' || v_b_list || ')';
ELSIF v_a_list IS NOT NULL and v_b_list IS NULL THEN
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ELSIF v_a_list IS NULL and v_b_list is not null THEN
v_sql_stmt := 'select distinct full_name from t_employee where gender in (' || v_b_list || ')';
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RETURN v_fullname_list;

I'd first recommend trying to avoid the dynamic sql.
use an approach like
[http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:210612357425] or
[http://stackoverflow.com/questions/1625649/oracle-parameters-with-in-statement/1655743#1655743] or [http://stackoverflow.com/questions/1715978/how-to-use-an-oracle-associative-array-in-a-sql-query]
but if that isn't in scope, do a
dbms_output.putline(v_a_list) ;
dbms_output.putline(v_b_list) ;
dbms_output.putline(v_sql_stmt) ;around and see what it emits

Unable to compile .ear file with an operation that returns an array

Hi
God, hopefully someone can help me.....
I have a web service that has various operations, one of which is attempting to return an array of strings. I am declaring a complextype in the WSDL that should functions as the array like this:
<schema.....
<element name="result" type="string"/>
<complexType name="searchResponseElement">
<sequence>
<element ref="tns:result" maxOccurs="unbounded"
minOccurs="0"/>
</sequence>
The error I receive is utterly vague, just saying ' compilation error occurred' when I go to deploy the ear file. I did have this working with another methos of declaring an array i.e.
<schema...
<complexType name="searchResponseElement">
<complexContent>
<restriction base="soap11-enc:Array">
<attribute ref="soap11-enc:arrayType" wsdl:arrayType="xsd:string[]"/>
</restriction>
</complexContent>
</complexType>
But, I was trying to consume the webservice in an APEX application and that method did not return a tree structure that APEX was able to handle.
I really am losing my mind over this as I've had the same type of definition working before. Please, anyone - any clues???

I answered this question that you also posted on stackoverflow.com.

Private inner class with private constructor

I read that if constructor is public then you need a static method to create the object of that class.
But in the following scenario why I am able to get the object of PrivateStuff whereas it has private constructor.
I am messing with this concept.
public class Test {
      public static void main(String[] args) {
           Test t = new Test();
           PrivateStuff p = t.new PrivateStuff();
      private class PrivateStuff{
           private PrivateStuff(){
                System.out.println("You stuff is very private");
}

A member (class, interface, field, or method) of a reference (class, interface, or array) type or a constructor of a class type is accessible only if the type is accessible and the member or constructor is declared to permit access:
* Otherwise, if the member or constructor is declared private, then access is permitted if and only if it occurs within the body of the top level class (§7.6) that encloses the declaration of the member or constructor. [Java Language Specification|http://java.sun.com/docs/books/jls/third_edition/html/names.html#6.6.1]
Your main method is within the body of the top level class, so the type (the inner class) and method are accessible.
eg:
class ImInTheSameSourceFileAsInnerAccessTest {
    public static void main(String[] args) {
        InnerAccessTest t = new InnerAccessTest();
        InnerAccessTest.PrivateStuff p = t.new PrivateStuff();
public class InnerAccessTest {
      public static void main(String[] args) {
           InnerAccessTest t = new InnerAccessTest();
           PrivateStuff p = t.new PrivateStuff();
      private class PrivateStuff{
           private PrivateStuff(){
                System.out.println("You stuff is very private");
}Result:
$ javac -d bin src/InnerAccessTest.java
src/InnerAccessTest.java:4: InnerAccessTest.PrivateStuff has private access in InnerAccessTest
InnerAccessTest.PrivateStuff p = t.new PrivateStuff();
^
src/InnerAccessTest.java:4: InnerAccessTest.PrivateStuff has private access in InnerAccessTest
InnerAccessTest.PrivateStuff p = t.new PrivateStuff();
^
2 errors
Edited by: pm_kirkham on 20-Jan-2009 10:54 added example of 'in the same source file'

Creating a generic class with a constructor that takes an array of objects

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