Java Literal And Assignment To Different Primary Types
Jan 20, 2015
I thought numeric literal were by default int or doubles, depending on if have a . and numbers after the But I wrote a quick test program as listed below. I understand the float float floatA = 5.5; failed to compile since 5.5 is a literal of type double and you are trying to assign this to a floag
What I am having problems with is byte byteA = 5; 5 is a literal of type int and this is being assigned to a byte and compiler should complain.The compiler does not allow two byte values to be added and assigned to a byte since the result of the addition is an int
class literalTesting{
public static void main(String[] arg){
byte byteA = 5; // allowed WHY I thought literal is an int and assigning int to byte
byte byteB = 10; // allowed
[code]...
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May 29, 2014
How do you do validation in java for primary key lets say the table got combination of two columns as primary key,how can i validate that if use enter already existing value...
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May 25, 2015
in Operator/Literals, it says "There is no literal representation for binary numbers in C, C++, or Java." seems "0b11001" could reprensent binary numbers?
int i = 0b100;
System.out.println(i);
the output should be 4.
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Oct 7, 2014
URL....So the problem is that when I type in "PA" it will display about 24 Zips and Populations before it stops. The problem is in the ZIPs file. It goes down the list and then takes the Zip from the Zips file to the Zips in the Population file and displays the Population. It will go to population 513 and stop. Reason being, there is no ZIP code in the Population file to display a population. The loop then stops. How can I get the program to skip over the zip code when there is no corresponding ZIP code in the other file and continue showing the other Pops..Here's what I currently have completed:
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class Population {
//Declaring global variables.
Scanner fileScannerZip, fileScannerPop, inputFile;
private String lineZip, linePop;
int invalidZip;
[code]...
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Oct 22, 2010
I am new with java, eclipse, jpa(eclipselink), postgresql, and trying to make a web application. I have two tables:
bids: id, quantity, price
trades: bidid, askid, quantity, price
bidid and askid columns are foreign keys from bids table (id), and they are the primary key for the trades table.
I created the Entities from the Tables (Bid and Trade class) with eclipse and it generated a TradePK class for the primary key.
Trade.java:
@Entity
@Table(name="trades")
public class Trade implements Serializable {
@EmbeddedId
private TradePK id;
[Code] ....
I understand that this is necessary because the primary key is from two column, but as soon I want to persist a Trade back to the database Eclipselink call the column names twice:
INSERT INTO trades (price, quantity, datetime, BIDID, ASKID, bidid, askid) VALUES (?, ?, ?, ?, ?, ?, ?)
So postgres give me back an exception: ERROR: column "bidid" specified more than once
And I don't know why. According to the JPA docs I didn't found any mistake:
Introduction to EclipseLink JPA (ELUG) - Eclipsepedia
Or I just can't see it... or is there a better doc which explains it better?
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May 30, 2014
i have a table with two columns as primary key i what to trap exception if the use in UI try to enter duplication in the table i don't what to throw ORA ERROR i what to display meaningful error massage,my database is oracle 11g
this is how i what to do it
i what to add integrity constraint to the table, and i use explicitly name it.
- i test the database to figure out what exception it returns for that constraint. With luck the name i used will be in the text of the exception.
- i add a catch to my database layer that catches SQLException, looks for the error message, and then throws a different exception, probably my own message
- In my UI layer catch that specific exception and convert it to something appropriate.
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Nov 21, 2014
I need to get a clone of a fairly deep object tree. All objects are entities and I need to set the primary keys to null. The root object:
public class Grundentscheidung implements Cloneable {
@OneToMany(cascade = CascadeType.ALL)
@JoinColumns({
@JoinColumn(name = "gesamtentscheidung_dstNr"),
@JoinColumn(name = "gesamtentscheidung_id")
[Code] .....
When I call
Grundentscheidung grundentscheidungClone = grundentscheidung.clone();
grundentscheidungClone contains the whole object tree with all dependencies, but the Tatbestand objects have their primary keys. When I use the debugger I see that Tatbestand.clone() is never called.
Is my code faulty? I would like to avoid to write a large method which sets all primary keys on the object tree to null.
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Apr 1, 2014
I am trying to understand the concept of Generics in java. In the introduction to Generic Types, this example is given:
Java Code: public class Box {
private Object object;
public void set(Object object) { this.object = object; }
public Object get() { return object; }
} mh_sh_highlight_all('java'); "Since
Since its methods accept or return an Object, you are free to pass in whatever you want, provided that it is not one of the primitive types." - I understand this.But then it has been changed to a generic class:
Java Code: /**
* Generic version of the Box class.
* @param <T> the type of the value being boxed
*/
public class Box<T> {
// T stands for "Type"
private T t;
public void set(T t) { this.t = t; }
public T get() { return t; }
} mh_sh_highlight_all('java'); "
As you can see, all occurrences of Object are replaced by T. A type variable can be any non-primitive type you specify: any class type, any interface type, any array type, or even another type variable."We can use any type in place of an Object, because Object is a superclass of all classes. But T (or any other class) is not a superclass of all classes. So how do we justify any class being used in place of a random T or any other class?
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Jun 26, 2014
I am looking at a snippet of code in my "learning Java 4th edition" by Orielly and there is a small snipped of code which says:
Java Code: Date date = new Date();
List list = new ArrayList();
list.add( date );
..
Date firstElement = (Date)list.get(0); // Is the cast correct? Maybe. mh_sh_highlight_all('java'); so I am typing the same thing in my compiler in a small Driver class and for some reason I have an error and Im dumbfounded...
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Jun 30, 2014
how many types of inputting method in java?can you explain with examples?
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Sep 7, 2014
I need to write a simple program that displays up to 5 pairings of data types (int, string) (string, long) ect. I need to have at least two classes, a Pair class (generic) and an PairTest class.
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Aug 25, 2014
I would like to create an ArrayList from data types stored in a text file.The ArrayList would be multidimensional with two data types; int, String.
Example text file could be:
4 cahiers grand format
3 stylots bic bleu
5 gommes
I find it very difficult for multiple data types i don't see how its possible.
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Mar 31, 2014
what is default literal for Boolean data type?
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Jun 3, 2014
char c=(char)-65;
This is legal but how ?? what is the value actually being stored in c ? The output is shown as .
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Jan 6, 2014
I have a program like below:
final String s1 = "AAA";
final String s2 = "AAA";
String s6 = s1+s2;
String s7 = "AAAAAA";
if ( s6 == s7 ){
System.out.println("s6 and s7 are same" );
}
On running, it prints "s6 and s7 are same". But if i remove the final modifier of s1 and s2 then it's not. What could be the reason?
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Sep 18, 2014
I need to use print not println to declare stuff and I need to have string literals I think that's /n. Now when I compile it just shows row1, row2 ect. Why does it work like that?
public class art {
public static void main(String[] args) {
//local variables
String row1= "***********************";
String row2= "** *** *** **";
String row3= "** ***** ***** **";
[Code] ...
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Apr 26, 2014
While doing trial and error got caught in the below scenario.
public class Crypt {
public static void main (String args[])
{
/*all I want is calculate a binary number (ex -: 22 , 34) using decimal base (10n).
*So, I have to convert 2 p into 10n form so I have to find n in terms of p . We have x as the input.
* The formula works as below.
*2p =10n
*p ln (2) =n ln (10)
*n = p [ln(2) / ln(10)]
*2 p = 10 p [ln(2) / ln(10)]
[Code] ....
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Mar 3, 2015
I'm trying to insert some data of type date into database table using hibernate.i take the input date from an xhtml form as shown below
addEvent.xhtml
Event Date (dd-mon-yy) :
<br/>
<h:inputText id="eventdate" value="#{eventBean.eventDate}" p:required="required"
p:type="date"/>
<p/>
<h:commandButton value="Add Event" actionListener="#{eventBean.addEvent}" />
<p/>
This is my addEvent method in EventBean.java
public void addEvent(ActionEvent evt) {
uname = Util.getUname();
boolean a = EventDAO.add(this);
if ( a) {
message = "Event has been added!";
[Code] ....
While executing this..i get the following error: ORA-01861: literal does not match format string. Could it be due to any mismatch in date format (chrome browser automatically takes date in the format mm-dd-yyyy )? If yes, how do I resolve it? (I'm using Oracle database)
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Apr 28, 2014
I am working with java project which is kind of charting room..but the problem is when am writing the query for listing the message in the conversation the error prevail in my eclipse...string literal is not properly closed by double quote...this is my java file
<%
String uname=session.getAttribute("username").toString();
String pword=session.getAttribute("password").toString();
java.util.Date dat=new Date();
int x=1;
try{
[code]....
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Jul 11, 2014
string literal is not properly closed by a double quote
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Apr 23, 2014
If you write
byte b = 100; it works (implicit conversion of implicit int literal 100 to byte.
But if you have a methodvoid bla(byte b){}
And want to invoke it with a literal (which is an int by default):bla(8) then there is no implicit conversion.
Is the byte b = 100; just an exception in Java? And is it the rule that one has to explicitely cast (narrow) integer literals when passing to smaller-than-int types?
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Sep 18, 2014
Here is the assignment:
Prompt the user to input two sides (a and b) of a right triangle. Calculate, using the
formulas below, the hypotenuse and the other two angles of the triangle. Calculate the
perimeter and the area.
Here are the formulas:
a^2 + b^2 = h^2
sinθ = a/h
A + B + C = 180 degrees
how to start this program out, i know which math classes i need to use.
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Jan 8, 2014
I just cant seem to understand the order of precedence here.
class Test{
public static void main(String[] args){
int k = 1;
k += (k = 4) * (k + 2);
System.out.println( k );
}
}
From what I have read compound operators have the lowest order of precedence... But the above piece of code makes the assignment k = 1 + (k = 4) * (k + 2) before evaluating the rest of the statement first.
It then evaluates (k = 4) and proceeds with the remained of the statement 1 + 4 * (4 + 6)....
I dont understand why the first k is assigned 1 but the remaining ks 4. Should they not all be 1 or 4 (I would have thought 4, since += has the lost order of precedence so is evaluated last)??
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Jun 14, 2014
I am working on the following java assignment..Write a program that randomly fills in 0s and 1s into a 4- by- 4 matrix, prints the matrix, and finds the first row and column with the most 1s. Here is a sample run of the program:
0011
0011
1101
1010
The largest row index: 2
The largest column index: 2
I have code that generates random 0s and 1s for the array, how to get the largest column and row.
import java.util.Random;
public class LargestRowColumn {
public static void main(String[] args){
//create 4x4 array matrix
int arrayMatrix[][] = new int[4][4];
[code]....
finding the row and column with the largest amount of 1s. I keep thinking well if I scan and find a one in the array, maybe I can just save the index of the row and column and then determine which index contains the most 1's after the array has been scanned.
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Apr 2, 2014
I'm trying to access the toolkit for an assignment I'm writing and I keep getting the same compiler message. What am I doing wrong?
import java.text.DecimalFormat;
import java.io.*;
import java.util.Scanner;
public class Robert_Gardner_6_07
{
public static void main(String[] args) throws IOException
[code]....
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May 17, 2014
I would like to know what is the significance of instantiating an object without an assignment.
I have created a class TestClass1 with a single constructor that prints a test message.
In TestClass2, if I write "new TestClass1()" rather than "TestClass1 x = new TestClass1()" it still works, and prints the test message.
I would like to know if I do not assign an object at the time of instantiation, it cannot be referenced or reused later, then what is the significance of this type of construct and when it can be useful, and where is the object being held.
public class TestClass1 {
TestClass1() {
System.out.println("This is a test message");
}
}
public class TestClass2 {
[Code] ....
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