Integer Sum In Generics
Mar 20, 2015What is wrong in this
class Gen<k,v>
{
K a;
V b;
Gen(K s, V f) {
a=s;
b=f;
[Code] .....
a is object of type k,then how can I retrieve content of a?
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Add Only String And Integer To ArrayList By Using JAVA GENERICS
Aug 27, 2014i am interested to add integer objects and String objects into any collection object ..... while iterating the collection object i am not interested to do any type cast in java
View Replies View RelatedCasting Exception In Generics
Jan 29, 2014I have studied that Generics are used to shift the Class Cast Exception into Compile time errors , So that we get errors at compile time error and we do correct them before executing ,but Here is a program in which i am getting Class Cast Exception
class Animal
{
}
class Dog extends Animal
{
}
class Cat extends Animal
[code]..
Getting Exception at line no 29 which i know why it occurs but just wanna ask that isn't it should be caught at compile time According to Generics ?
Clarify Generics For Classes
Jun 19, 2014I just want to clarify generics for classes.
Referring to [URL] ....
Generics means all methods in class Box will return an Integer if their parameters are defined as T when the instantiation is :
Box<Integer> integerBox = new Box<Integer>();
Are those Boxes only can contain Integers? Can I write
Box <Toys> toybox = new Box <> ();
To show that the Box only contain toys?
Java Generics Super And Ext
Jun 17, 2014Set<? super TreeMap> s = new HashSet<SortedMap>();
SortedMap<String,String> sm = new TreeMap<String,String>();
TreeMap<String,String> tm = new TreeMap<String,String>();
s.add(sm); //This fails
s.add(tm);
Why does adding sorted map to a Set that allows ? super TreeMap and instantiated as such fail?
Returning Int Array Using Generics
Apr 10, 2014public int[] allIndicesOf(E itemSought) {
ArrayList<Integer> toUse = new ArrayList<>();
for (E anArray : container) {
if (anArray.equals(itemSought)) {
toUse.add(container.indexOf(itemSought));
[Code] ....
I have an array list of strings. I want to be able to return an array of integers telling me which indexes in the string array list contain the itemSought object.
Generics Super Keyword
Feb 14, 2014Suppose I have
class A {
public void speak() {
System.out.println("I am class A");
}
}
class B extends A{
public void speak() {
System.out.println("I am class B");
}
}
class C extends B{
public void speak() {
System.out.println("I am class C");
}
}
Why this doesn't work while A is a super type of B ?
public static void insertElements(List<? super B> list){
list.add(new A()); //not OK, why?
}
Why Use Extends Keyword Instead Of Implements In Generics
Feb 22, 2015Why java uses the keyword extends when setting the bound of a type parameter(Generic) to an interface. I think using the keyword implements is more intuitive.
public static <T extends Comparable<T>>
why use extends? and not implements.
int countGreaterThan(T[] anArray, T elem) {
int count = 0;
for (T e : anArray)
if (e.compareTo(elem) > 0)
++count;
return count;
}
I know if I want to set multiple bounds I will use extends keyword, and I will concatenate the bounds using & operator.
Is this a design decision to always use extends keyword to set bounds?
Generics Wildcard Array Of References?
Jul 27, 2014An array of references to a specific generic type is not allowed in Java.
e.g.,
ArrSpec<String> arrs[] = new ArrSpec<String>[10];
is not allowed though the type checkng and memory allocation can be done at the compile time itself.
Instead of this, Java allows to use Wildcard type array of references to a generic type.
e.g.,
ArrSpec<?> arrs[] = new ArrSpec<?>[10];
is allowed though the type checking, memory allocation and any type of values to be stored would be decided at the runtime.
Generics In Java - E Is A Subtype Of Comparable
Jun 5, 2015My book defines this generic method
Java Code:
public static <E extends Comparable<E>> void sort(E[] list... mh_sh_highlight_all('java');
Comparable is an interface and from how i look at this piece of code is that I can only use a class that implements the Comparable interface; however, this is the context my book uses when explaining the following code
First, it specifies that E is a subtype of Comparable.
Second, it specifies that the elements to be compared are of the E type as well.
What does it mean when it says E is a subtype.
Generics And Inheritance - Specialized Methods
Mar 6, 2014I've an interface with generic methods in it. I would like to have specialized methods in the sub types. While doing that I'm seeing the following warnings in eclipse.
class Sorter {
<E> void sort(E[] elements);
};
class StringSorter {
// This gives me a warning 'hiding' to 'sort'
<String> void sort(String[] elements) {
}
// Gives me an error "The method someCrap(String[]) in the type StringSorter is not applicable for the arguments (String[])"
void someCrap(String[] elements) {
}
};
I would like to understand why eclipse gives the above warnings and errors.
Upcasting And Downcasting Rule For Object And Generics?
Dec 15, 2014is the Java upcating and downcasting rules are same for general object type or generics types?
1) Dog dog = new Animal();
Type mismatch can't covert Dog to Animal - complie time error
2) Animal animal = new Animal();
Dog dog = (Dog) animal;
java.lang.ClassCastException: Animal cannot be cast to Dog at runtime.
Doubly Linked Lists And Using Java Generics
Oct 25, 2014I'm working with Doubly Linked Lists and using Java Generics..
My nodes looks like this:
class DNode<E> {
DNode<E> previous;
DNode<E> next;
E element;
//and all methods inside
}
My list of Nodes looks like this:
class DLL<E>{
private DNode<E> head;
private DNode<E> tail;
private int size;
[code]....
As you can see, as arguments they get "E o"...I need to write a program, which from the main function asks the users how long is the list, and after they type it's length, I ask them to start typing the elements (integers)...and this is how my main method is written, but I can't seem to make it work, specialy when I call the "insLast" method,I guess it's because the arguments i'm giving to the function...how to read the elements and write them into the list?
public static void main(String[] args) throws IOException {
DLL<Integer> lista=new DLL<Integer>();
BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
String s = stdin.readLine();
int N = Integer.parseInt(s);
s = stdin.readLine();
String[] pomniza = s.split(" ");
for (int i = 0; i < N; i++) {
lista.instLast(Integer.parseInt(pomniza[i]));
}
}
First Time Using Generics - Incomparable Type Errors
Aug 29, 2014I am trying to make a generic method that will replace the data type T with those number types usable with a Scanner object. However, whenever I try to compile, I get errors saying that a Byte/Integer/Double etc are found when only a type T is allowed. This is the beginning of my method. I can;t understand what is wrong with it.
Java Code:
public <T extends Number> T nextRanged(T lowerBound, T upperBound, boolean inclusive, String errorMessage){
// Holds program execution until user inputs a numeric value between the bounds. Prevents all other input without exception.
// Output data type determined by the type of the bounds.
T input = null;
try{
if(input instanceof Byte){
input = new Byte(internalScanner.nextByte());
[Code] ....
The purpose of the method, in the end, will be to provide the nextXXX() functionality of a Scanner object but with built in validation procedures. I could easily do this by making a nextIntRanged(), nextDoubleRanged() etc methods, but this seems wasteful to me.
I meant "incompatible type errors"!
Error example:
ValidatedScanner.java:57: error: incompatible types
input = new Byte(internalScanner.nextByte());
^
required: T
found: Byte
where T is a type-variable:
T extends Number declared in method <T>nextRanged(T,T,boolean,String)
Erasure Feature From Generics - Duplicated Bound Error
Jun 14, 2014The erasures of all constituent types of a bound must be pairwise different, or a compile-time error occurs.
Well I know what type erasure is, and I think I kind got what this statement means. My understanding from it is that if your type parameter has more than one bound and those bounds occurs to be the same type after erasure that is a compile-time error. Is that it?
The only thing I could found related is something like this:
class A<T extends List<Integer> & List<Integer>>{
}
Which as you might know gives the Duplicated bound error.
Java Generics - Why Cannot Use Primitive Data Type Like Int / Double
Feb 21, 2014I have doubt in generics,
List<int> c=new ArrayList<int>();
why we cannot use primitive data type like int,double.
Can't Seem To Get Value For Integer 1 And Integer 2 To Pass With SetValue Method
Aug 10, 2014public class MyInteger {
private int value;
public MyInteger(int number){
value = number;
System.out.println("Constructor created with value of " + value);
[code]....
I can't seem to get the value for integer1 and integer2 to pass with the setValue method. I get a runtime error stating the I need to have an int value for these two integers.
How To Validate And Integer From 0 - 9
Nov 5, 2014I created a GUI with a jTextField as an input box and am wondering how to validate that this data is an integer from 0 - 9. Here is what I have. However the if statement shows an error that says int cannot be dereferenced.
private void doneButtonActionPerformed(java.awt.event.ActionEvent evt) {
//Create and Initialize Variable
int category = Integer.parseInt(categoryInput.getText());
if (category.matches(0-9)); //int cannot be dereferenced error here
{
[Code]...
How To Split The Integer
Jul 9, 2014I am trying to split an integer for example my input is 0590
I want the output as
0
5
9
0
How to do this.
String In Integer Possible?
Apr 29, 2014Code:
public static void main(String[] args) {
// TODO code application logic here
Calendar time = Calendar.getInstance();
int min = 1;//time.get(Calendar.MINUTE);
String blank = "0";
int checker = ((min > 10 ) ? min : blank+min);
System.out.println("The time is " + "12" + ":" + checker );
}
This is my code, as you can see, I have if the min is less than 10, display the string "0" next to it so it will be something like
blank is zero and min is one
So it will display as 01 but after min reaches 10 and above, the 0 goes away. Problem I have is, you just cant add "blank" to int checker because checker is an int and blank is a string. So what must I do in order for it to display the 0 under checker?
Integer Or Int For Loops
Mar 4, 2014I would like to know which one is more appropriate to use in "for" loops or "while" loops.I don't know exactly when to use Integer or int.
for(int i=0; i<10; i++){ ... }
for(Integer i=0; i<10; i++){...}
Search For Key In Integer Array?
Jun 29, 2014// 1 ***** student writes this method
/** Searches for key in integer array named arr
// arr is an instance variable of the class and has been instantiated and filled with random values.
// @param key value to search for
// @return if key is found, the index of the first element
// in array whose value is key; if key is not found,
// the method returns -1
*/
public int sequentialSearch( int key ) {
// Note: To animate the algorithm, put this method call as the first statement in your for loop
// animate( i, 0 );
// where i is the index of the current array element
return 0; // replace this statement with your return statement
} // end of sequentialSearch
[Code] ....
Exception With Array Of Integer
Mar 3, 2014I'm trying to insert numbers in a array of Integer neatly. When i try to insert the following numbers i have this exception.
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at time.Historico.insere_ordenado(Historico.java:35)
Line 35 in my code is:
"while (num >= arry[i] && arry[i] != null && i < arry.length - 1)"
Numbers:
71516357248031
I have this exception when i try to instert 80.
public Integer[] insert_neatly(Integer[] arry, Integer num)
{
Integer i, acum, aux, temp;
i = acum = 0;
if (arry[i] == null)
[Code] ....
What is wrong with this code?
How To Print Big Integer Using For Loop
Mar 6, 2015I amtrying to iterate a value of L,R both are range of BigInteger but its not working
BigInteger L=in.nextBigInteger();
BigInteger R=in.nextBigInteger();
for (BigInteger bi =L;
bi<=bi.compareTo(R);
bi = bi.add(BigInteger.ONE)) {
//Task to do with Numbers
}
I am trying to iterate a for loop in range of L and R but its not working
Digit Sum Of Integer Is Sum Of All Digits
Oct 13, 2014Digit sum of an integer is the sum of all its digits. For example, the digit sum of 123 is 1+2+3 = 6
and the digit sum of 99 is 9 + 9 = 18.
But how to write the programm that will count those numbers?
Traversing Integer Array?
Mar 27, 2014class Test {
public static void main(String[] args) {
int arr[]={1,2,3,4,5};
int search = 5;
int i=0;
boolean flag=false;
[Code] .....
Above program runs fine.Above in each iteration we have 2 conditions, first to check if iteration number is less then array length and second is to match it with the search integer.I am required to reduce these two conditions and make it one only.Have tried it but no success.