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What is the difference between up-casting and down-casting with respect to class variable
...use
Downcasting(or narrowing), and Downcasting is not directly possible in Java, explicitly we have to do.
Dog d = new Dog();
Animal a = (Animal) d; //Explicitly you have done upcasting. Actually no need, we can directly type cast like Animal a = d; compiler now treat Dog as Animal but still it i...
Replace String in all files in Eclipse
...fill the search box
In the “File name patterns” input box, type in “.java” for replacing all Java files or type in "" to replace in all files
Click “Replace…”
Ctrl+V (Paste). Or type in the value you want to do the replacing
Enter
You can find more details in my blog post: http://bl...
How can prepared statements protect from SQL injection attacks?
...uding the information about Aaron which was supposed to be hidden.
import java.sql.*;
public class Inject {
public static void main(String[] args) throws SQLException {
String url = "jdbc:postgresql://localhost/postgres?user=user&password=pwd";
Connection conn = DriverMan...
How to compare objects by multiple fields
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With Java 8:
Comparator.comparing((Person p)->p.firstName)
.thenComparing(p->p.lastName)
.thenComparingInt(p->p.age);
If you have accessor methods:
Comparator.comparing(Person::getFirstName)
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Remove elements from collection while iterating
... new elements during iteration.
Using JDK >= 8
For those working with Java 8 or superior versions, there are a couple of other techniques you could use to take advantage of it.
You could use the new removeIf method in the Collection base class:
ISBN other = new ISBN("0-201-63361-2");
books.re...
Generating all permutations of a given string
...a and ab , but what about longer string such as abcdefgh ? Is there any Java implementation example?
52 Answers
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Backing beans (@ManagedBean) or CDI Beans (@Named)?
I've just started reading through Core JavaServer Faces, 3rd Ed. and they say this (emphasis mine):
5 Answers
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Why is Class.newInstance() “evil”?
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The Java API documentation explains why (http://java.sun.com/javase/6/docs/api/java/lang/Class.html#newInstance()):
Note that this method propagates any exception thrown by the nullary constructor, including a checked excepti...
Redirect to an external URL from controller action in Spring MVC
...be taken as default, if the added thing is value ?
– JAVA
Sep 14 '18 at 12:14
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compareTo() vs. equals()
When testing for equality of String 's in Java I have always used equals() because to me this seems to be the most natural method for it. After all, its name already says what it is intended to do. However, a colleague of mine recently told me had been taught to use compareTo() == 0 instead of ...