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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...
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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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...
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 ...
Is SonarQube Replacement for Checkstyle, PMD, FindBugs?
... as a few other "plugins" such as Cobertura (code coverage) by default for Java projects. The main added value, however, is that it stores the history in a database. You can then see the trend. Are you improving the code base or are you doing the opposite? Only a tool with memory can tell you that.
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