Section 1
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What is method overrriding and method overloading?
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Section 1
(50 cards)
What is method overrriding and method overloading?
Method over riding is a sub class having the same method signature as they're super class but different implementation. Method over loading is a class having the same method name with different amount of parameters.
Assuming a method contains code which may raise an exception, but not a Runtime Exception, what is the correct way for the method to indicate that it expects the caller to handle that exception?
in the method signature you can throws exception
What is the differences between String, String Builder, and String Buffer?
Strings are immutable. String Builder and String Buffer are mutable. String Builder is not synchronized. String Buffer is synchronized.
Why are strings immutable?
Strings cannot change once they are created. This is because multiple references point to the same string in the string pool and if one reference changes the string, the other references would point to this changed string. Strings are immutable to conserve memory.
Is java pass by value or pass by reference?
Java is pass by value. A copy of the the callers parameters are passed.
What is the difference between HashTable and HashMap?
HashTable is synchronized. HashMap is not synchronized. HashTable does not allow null values. HashMap allows null values and the null key.
How do you clone an object?
Mark the class cloneable. Invoke the clone method. The clone method makes a shallow copy of the object which means it makes a copy of the reference.
What are some Thread methods?
start. sleep. yield. join. isAlive.
How do you get the size of an array arr?
arr.length;
What is stored on the stack and what is stored on the heap?
Stack allocates memory for methods, references, and primitives. It is used for static allocation. Heap allocates memory for objects and anything using the new call. It is used for dynamic allocation. Garbage collection is ran on the heap. Threads have their own stack.
What is the difference between Statement and Prepared Statement?
Both are interfaces of jdbc. A statement is used for single sql statements. A prepared Statement is used to execute a sql statement that will be used many times. A prepared Statement is used to prevent sql injection. a prepared Statement is used when you need to pass parameters to the query at run time.
What is the difference between ArrayList and Vector?
ArrayList is not synchronized. Vectors are synchronized and thread safe.
What is the difference between == & .equals()
"==" checks to see if two references point to the same instance of an object. equals() checks to see if two objects are equal, but they don't have to point to the same instance of the object.
Does an unchecked exception have to be dealt with a try catch block?
No. Unchecked exceptions are compile time exceptions.
Are String and String Buffer mutable?
No. Strings are immutable. String Buffer is mutable and synchronized.
Can a sub class access private members of the super class?
No. A sub class in a different package can access protected and public members of a super class.
Does a try block need a catch block?
No. a try block can have a catch and/or a finally block.
What are transient variables
Transient variables are variables that are not serializable.
How can you create a thread?
Extend the thread class and override the run method. Implement the Runnable interface and pass an instance to the thread constructor.
Does a Set have to contain unique elements?
Yes.
How do you serialize an object?
Use the Serializable marker interface on a class. Create an object of the class and persist it using the java.io.OutputStream class.
What memory areas are allocated by the JVM?
Stack Heap PC Register Class Loader Class Area Execution Engine
What is polymorphism? Give an example.
Polymorphism is the ability of inherited methods to change their behavior depending on what subclass they are in. Example: Cat and Dog inherit from Pet, but the method make Sound would be different in the sub classes.
What are the different types of polymorphism.
Method overloading and overriding. Method over loading is compile time. The compiler checks the number of parameters. Method over riding is run time. The overridden code in the method is ran.
What are the implicit modifiers required for interface variables?
static final static to make it global final to make it constant
What is the difference between TreeSet and HashSet?
HashSet is faster than TreeSet. HashSet has no ordering guarantees, but TreeSet does. HashSet has constant time operations. TreeSet has log time operations.
What is encapsulation? Give an example
Encapsulation is the binding of instance methods with a class. Access to the data and code is controlled by a barrier. Example: creating getters and setters for a class to restrict access to the instance variables.
How can a final variable be initialized when its declared in a class?
Initialized in line: final int MAX = 5; Initialized in each constructor Initialized in a non static block
What are the differences between array and Array List?
Arrays are static in size. Array Lists are dynamic. Arrays are multi dimensional. Array Lists are single dimensional. Both can store null and duplicate values.
What is final, finalize(), and finally?
final is a keyword that can be used on classes, methods, and variables. Final classes can't have subclasses. Final methods can't be overridden. Final variables can't be changed. finalize is a method used by the garbage collector before it collects non referenced objects. finally is part of a try catch block that runs regardless if an exception is caught.
What is a stored procedure and how do you call it from a java class?
A stored procedure is an executable block of code written in pl/sql. You call a stored procedure using the callableStatement interface of jdbc.
What is the thread lifecycle?
Thread lifecycle : Runnable Blocked Waiting Terminated
Do you need to initialize an object to call a static method?
No. You can call a static method by using class.staticMethod(). If you are in the class, you can just call staticMethod().
What is the difference between an interface and an abstract class
An interface only has abstract methods. An abstract class can have abstract classes and concrete methods. Every interface method must be overridden. There are functional and marker interfaces. Interfaces can extend multiple other interfaces. Since java 8, interfaces can have default methods that don't need to be overridden.
Can you name some differences between Linked List and Array List?
Searching is faster in Array Lists than Linked Lists. Deletion is faster in Linked Lists than Array Lists. Insertion is faster in Linked Lists than Array Lists.
What is a marker interface?
A marker interface has no methods. It is used to specify classes that should have additional functionality. Example: serializable, remote, cloneable
What is inheritance? Give an example.
Inheritance is the ability of sub classes to inherit functionality from they're super class. This promotes code reuse. Example: A boss implements the characteristics of an employee, but has more characteristics.
What is the difference between static and final variables.
Static variables are global and there is only a single instance of it. Final variables cannot be changed.
What is a wrapper class?
A wrapper class encapsulates the functionality of a class. A wrapper class gives primitive data types object behavior.
Do Objects added to a TreeSet require implementations of Comparable
TreeSet inherits from Comparable interface
Can you force garbage collection?
No. You can request garbage collection using System.gc().
Can you perform operator overloading?
No. Java does not support it like C does.
What is the difference between List and Set
A List allows duplicates. A set does not allow duplicates. If a duplicate tries to enter the array, it is ignored and no error is thrown.
What Collection would not allow duplicate elements?
Set Collection interface does not allow duplicates. When you try to add a duplicate, it ignores it and does not throw an error.
What is a class?
A class is the blueprint to an object.
What are the access modifiers?
public: accessible anywhere in the program. protected: accessible to the packages and subclasses outside the package. default: accessible to the package only. private: accessible to the class only.
What are some classes that implement SortedSet
TreeSet ConcurrentSkipListSet
What are constructors and when are they called?
A constructor is a block of code similar to a method, except it doesn't have a return type. It is called when an instance of an object is instantiated. A constructor has the same name as a class. The default constructor is given if no other constructors are written and takes no parameters. Constructors return objects, or return an exception. they cant return null.
Can you describe singletons?
Singletons is a design pattern. A singleton is when you create a single instance of something.
What is the Reflection API?
Reflection gives java run time knowledge of its methods and variables. Benefits: extensible features and debugging. Drawbacks: overhead and security risks.
Section 2
(50 cards)
What are the non access modifiers?
Non access modifiers provide functionality to classes, methods and variables. Static: allows access without creating an object instance Final: finalizes the implementation. Synchronized: prevents threads from accessing resources at the same time. Transient: prevents method from becoming serialized. Volatile: makes class thread safe.
List some object methods
hashCode. clone. equals. finalize. getClass. notify. notifyAll. toString. wait.
Can you explain threads?
A thread is an independent path of execution in a program. A thread has its own stack. Threads share resources. Threads are lightweight compared to processes.
Can you explain exceptions?
Exceptions are events that occur during the execution of a program that inturrupt the flow of operations. An Exception is an object that wraps an error event within a method that contains information about the error.
What is the root interface of the Collection API
Collection
What are intrinsic locks?
Intrinsic locks enforce exclusive access to thread resources. Synchronization is built around intrinsic locks.
What are unchecked exceptions?
Unchecked exceptions are exceptions that inherit from Error or RuntimeException. Code still compiles if there is an unchecked exception. unchecked exceptions are: StackOverflowError. NullPointerException. ArrayIndexOutOfBoundsException. NumberFormatException.
What is included in the JDK?
JRE Garbage Collector JVM
Does the Comparator interface declare the compareTo method?
No! The Comparable interface implements the compareTo method. The Comparator interface implements the compare method. compareTo method is used to define the Natural order an object, using by its ID. compare method is used to define other ways to compare two objects. compare method is used when you do not have access to the two classes you want to compare.
What are virtual methods?
A method which can be overridden.
What are the primitive data types?
byte short int long boolean char float double
What is abstraction? Give an example.
Abstraction is hiding the complex functionality of a method, while providing a simple method signature. Example: a remote control hides the complex details while giving an easy way to use it.
Can the finalize method be overriden?
Yes. If an object has a lock on a file or database table, you would want to override the finalize method to release the resources those objects are holding onto when the object is garbage collected.
What are the differences between throw and throws?
Throws is used to declare an exception. Throw is used to throw an exception explicitly. Throws is used in the method signature. Throw is used in the method body. Example: public void shutdown() throws Exception { throw new Exception("unable to shutdown"); }
Where does the run method come from?
run method comes from the Runnable functional interface.
Can the synchronized keyword be used for a class?
No. It can only be used for methods and code blocks.
Explain the JVM, JRE, and JDK
The JVM is the operating system java programs run on. The JRE is what java needs to run a java program. The JDK is the development environment a java program needs.
When is garbage collection ran?
Before an OutOfMemoryException is thrown.
What are checked exceptions?
Checked exceptions are forced by the compiler. Checked exceptions must be handled by a try catch block or be specified in the method signature. Checked exceptions: IOException. ServletException. FileNotFoundException Exception. ClassNotFoundException. ParseException. InstantiationException.
What are short circuits?
|| and &&
What is in-variance?
Is map part of Collection?
No. It is part of the Collection framework, but it does not implement the java.util.Collection Interface. Maps work with key value pairs.
How do you prevent deadlock?
Synchronization
Does every method in a class that extends serializable need to implement serializable?
No. Not every method needs too.
The changes to the instance variables of one object also change the instance varialbes of another object?
No. Instance variable values are instance specific and are not shared among instances.
What are the states of a thread
Runnable Blocked Waiting Terminated
What is deadlock?
Deadlock is when two threads are holding resources that the other needs.
What is the benefits of Generics?
Generics provide compile time safety. Generics eliminate the need of casts. Generics provide stronger type checks.
What is Generics?
Generics allow methods to operate on objects of various types while providing compile time safety. This makes java a fully statically typed language.
Why do we use OOP?
OOP is good coding practice and makes large programs understandable and maintainable.
Explain the Throwable heirarchy.
Throwable branches to Error and Exception. Error exceptions are unchecked exceptions. Exception branches to checked exceptions and RunTimeException RunTimeException exceptions are unchecked exceptions.
Can java programs control thread scheduling?
Yes. Java programs can create, run, and manipulate threads
What is co-variance?
How do you invoke a static method?
class.staticMethod() you dont need to create an instance of the class.
List some string methods
equals. toUpperCase. toLowerCase. compareTo. compare. concat. split. length. replace. intern.
What is autoboxing?
Autoboxing is javas way of wrapping a primitive into its wrapper class automatically to give it object funtionality. Example: autoboxing: Integer a = 2; unboxing: int b = 5 + a
What is the continue statment used for?
the continue statement causes the loop to immediately jump to the next iteration of the loop
Can you name a class that does not inherit from Iterable?
HashTable
Can you explain the Collection Framework?
The Java Collection Framework, JCF, is a collection of interfaces that implement commonly used data structures. The three main sub interfaces are List, Set, Queue
Can static methods be overridden?
No. overridden methods happen at run time. static methods are looked up at compile time.
What is the Comparator interface used for?
The Comparator interface has the method compare(T obj1, T obj2) which should be used to make serveral sort methods to compare objects based on instance variables.
What is serialization used for?
It is used to send objects in byte stream form across a network. Benefits: Persists the state of objects. Platform independent.
for loop vs while loop
In a for loop, you define the variable, the condition, and how the loop should increment. In a while loop, you only define the condition
What are the differences between collection and collections?
Collection is an interface for collection classes. Collection interface defines methods common to structures which hold objects. List, Set, Queue are sub interfaces of collection. Collections is a utility class. Collections has static methods for doing operations on objects Collections has a method for finding the max element in a Collection. It also has sort method
What is the Comparable interface used for?
The Comparable interface has the method obj1.compareTo(T obj2) which should be used to compare objects based on user defined methods.
Explain OOP
OOP stands for Object Orientated Programming. OOP is creating parts of the program to act as objects that interact with each other. The pillars of OOP are abstraction, encapsulation, inheritance, and polymorphism.
What is new to java 8?
Lambda expressions. Interface default methods.
What are some benefits of the JCF?
The JCF reduces programming effort. The JCF promotes code reuse. The JCF allows developers to settle on a single way that data structures should be written.
Can you explain Serialization?
Serialization is converting methods into a byte stream that can be reverted into a copy of the code.
What does javac do?
javac compiles .java files into .class files which is byte code instructions for the JVM.
Section 3
(15 cards)