Java interview questions
- How to retrieve a key and Value from a map ? view answer
- Why can an interface supertype call methods that belong to Object class? view answer
- Q. What is difference between shallow copy and deep copy ? view answer
- Q.Why to override equals() and hashCode()? and How i can implement both equals() and hashCode() for Set ? view answer
- Q.How to sort list of objects ( User Defined) using comparator? in Descending Order. view answer
- Q. How to sort list of objects ( User Defined) using comparator?
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- What is the difference between int and Interger? view answer
- Singleton Double-checked locking in Java?
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- What are the parameters to follow Creating and Destroying Objects in Java? view answer
- Q.What are the different scopes for Java variables?
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- Q.What method must be implemented by all threads?
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- Q.Can an unreachable object become reachable again?
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- Q.What are the steps in the JDBC connection?
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- Q.How are this() and super() used with constructors?
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- Q.What is the difference between static and non-static variables?
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- Q.What is the purpose of finalization?
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- Q.Does garbage collection guarantee that a program will not run out of memory?
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- Q.What is synchronization and why is it important?
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- Q.What is daemon thread and which method is used to create the daemon thread?
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- Q.What are synchronized methods and synchronized statements?
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- Q.If I write System.exit (0); at the end of the try block, will the finally block still execute?
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- Q.If I write return at the end of the try block, will the finally block still execute?
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- Q.Is it necessary that each try block must be followed by a catch block?
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- Q.What is the basic difference between the 2 approaches to exception handling.
1> try catch block and
2> specifying the candidate exceptions in the throws clause?
When should you use which approach?
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- Q.What are the different ways to handle exceptions?
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- Q.What is the difference between error and an exception?
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- Q: What is wrapper class? Explain with example? view answer
- Q.What is serialization? Explain with example? view answer
- Q.What one should take care of while serializing the object?
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- Q. When you serialize an object, what happens to the object references included in the object?
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- Q.What happens to the static fields of a class during serialization?
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- Q. Objects are passed by value or by reference?
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- Q. Primitive data types are passed by reference or pass by value?
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- Q. What type of parameter passing does Java support?
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- Q.Can a top level class be private or protected?
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- Q.What is the default value of an object reference declared as an instance variable?
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- Q.What is the difference between declaring a variable and defining a variable?
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- Q. What are different types of inner classes?
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- Q. What is Overriding? view answer
- Q.What are Checked and UnChecked Exception?
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- Q. What is final?
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- Q.What is static in java? view answer
- What is an abstract class?
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- Q. What are the modifiers in Java ? view answer
- Q.Difference between HashMap and HashTable? view answer
- Q.Difference between Vector and ArrayList? view answer
- Q.Difference between ArrayList and LinkedList? view answer
- Q.What are pass by reference and passby value in Java? view answer
- Q. When we go for Abstract and Interface in Java? view answer
- Q.What is the difference between interface and abstract class? view answer
- Q.What are the Garbage collection algorithms in Java? view answer
- Q.What is garbage collection and the purpose of garbage collection in Java? view answer
- Q. What is the difference between an Interface and an Abstract class?
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!!! Java interview questions !!!
Q.How to sort list of objects ( User Defined) using comparator? in Descending Order.
Q. How to sort list of objects ( User Defined) using comparator?
You can use Collections.sort(List,Comparator) to sort objects.
Example : You have User Bean , you want to sort based on username filed.
User Class :
public class User {
String userName = "";
String city = "";
String state = "";
/** * @return Returns the userName.
*/
public String getUserName() {
return userName;
}
/**
* @param userName The userName to set.
*/
public void setUserName(String userName) {
this.userName = userName;
}
}
Then you have to write a comparator class.
public class UserNameComparator implements Comparator {
public int compare(Object user, Object anotherUser) {
String firstName1 = ((User) user).getUserName().toUpperCase();
String firstName2 = ((User) anotherUser).getUserName().toUpperCase();
return firstName1.compareTo(firstName2);
}
}
Now sorting code
User user1 = new User();
user1.setUserName("das");
User user2 = new User();
user2.setUserName("nick");
User user3 = new User();
user3.setUserName("ram");
User user4 = new User();
user4.setUserName("jadu");
ArrayList list = new ArrayList();
list.add(user1);
list.add(user2);
list.add(user3);
list.add(user4);
Collections.sort(list,new UserNameComparator()); // sort ascending order.
// Descending order
Collections.reverse(list);
for(int i=0;i<list.size();i++){
User usr = (User)list.get(i);
System.out.println(usr.getUserName());
}
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