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30 Cards in this Set

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What are the primitive types and their sizes?
I EIGHT a BYTE but was SHORTed 16 bits INT-to 32 of those LONG 64's that FLOATed 32 bits while DOUBLE-ing 64 of them.
They just didn't have the CHAR-acter of the 16's.
How could Java classes direct program messages to the system console, but error messages, say to a file?
The System class has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This how the standard output could be re-directed:
Stream st =
new Stream (new
FileOutputStream ("techinterviews_com.txt"));
System.setErr(st);
System.setOut(st);
Explain the usage of the keyword transient?
This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers).
How do you know if an explicit object casting is needed?
If you assign a superclass object to a variable of a subclass’s data type, you need to do explicit casting. For example:
Object a;Customer b; b = (Customer) a;
When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.
What’s the difference between the methods sleep() and wait()
The code sleep(1000); puts thread aside for exactly one second. The code wait(1000), causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.
Can you write a Java class that could be used both as an applet as well as an application?
Yes. Add a main() method to the applet.
What’s the difference between constructors and other methods?
Constructors must have the same name as the class and can not return a value. They are only called once while regular methods could be called many times.
Can you call one constructor from another if a class has multiple constructors
Yes. Use this() syntax.
Explain the usage of Java packages.
This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. The default access level also allows you to protect data from being used by non-authorized classes.
If a class is located in a package, what do you need to change in the OS environment to be able to use it?
You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Let's say a class Employee belongs to a package com.xyz.hr; and is located in the file c:/dev/com.xyz.hr.Employee.java. In this case, you’d need to add c:/dev to the variable CLASSPATH. If this class contains the method main(), you could test it from a command prompt window as follows:
c:\>java com.xyz.hr.Employee
What would you use to compare two String variables - the operator == or the method equals()?
I’d use the method equals() to compare the values of the Strings and the = = to check if two variables point at the same instance of a String object.
Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?
Yes, it does. The FileNoFoundException is inherited from the IOException. IOException’s subclasses have to be caught first.
Can an inner class declared inside of a method access local variables of this method?
It’s possible if these variables are final.
What can go wrong if you replace && with & in the following code:
String a=null;
if (a!=null && a.length()>10)
{...}
A single ampersand here would lead to a NullPointerException.
What’s the main difference between a Vector and an ArrayList
Java Vector class is internally synchronized and ArrayList is not.
When should the method invokeLater() be used?
This method is used to ensure that Swing components are updated through the event-dispatching thread.
How can a subclass call a method or a constructor defined in a superclass?
Use the following syntax: super.myMethod(); To call a constructor of the superclass, just write super(); in the first line of the subclass’s constructor.
What’s the difference between a queue and a stack?
Stacks works by last-in-first-out rule (LIFO), while queues use the FIFO rule.
You can create an abstract class that contains only abstract methods. On the other hand, you can create an interface that declares the same methods. So can you use abstract classes instead of interfaces?
Sometimes. But your class may be a descendent of another class and in this case the interface is your only option.
What comes to mind when you hear about a young generation in Java?
Garbage collection.
What comes to mind when someone mentions a shallow copy in Java?
Object cloning.
If you’re overriding the method equals() of an object, which other method might you also consider overriding?
hashCode()
You are planning to do an indexed search in a list of objects. Which of the two Java collections should you use: ArrayList or LinkedList?
ArrayList
How would you make a copy of an entire Java object with its state?
Have this class implement Cloneable interface and call its method clone().
How can you minimize the need of garbage collection and make memory use more effective?
Use object pooling and weak object references.
There are two classes: A and B. B needs to inform A when some important event has happened. What Java technique would you use to implement it?
If these classes are threads I’d consider notify() or notifyAll(). For regular classes you can use the Observer interface and pattern.
What access level do you need to specify in the class declaration to ensure that only classes from the same directory can access it?
You do not need to specify any access level, and Java will use a default package access level.
What is inheritance.
Inheritance is where objects of a sub-type can inherit and re-use properties and functions of a super-type. For example, ducks generally speaking, fly so a Mallard duck could inherit the flying behavior from the generic Duck type.
What is polymorphism?
Polymorphism refers to the capability of sub-types to use different variations of behavior than their super types, in some cases the behavior is completely different or even non-existent. This is done through method overriding, overloading or aggregation wherein a method has additional behavior rather than different behavior.
Whats the difference between final, finally and finalize?
final – Applied to a member variable means the variable may not be initialized more than once. Applied to a class means it may not be extended. Applied to a method means the method may not be overridden.

finally – The finally block always executes when the try block exits, excepting the System.exit(0) call. This ensures that the finally block is executed even if an unexpected exception occurs. But finally is useful for more than just exception handling — it allows the programmer to avoid having cleanup code accidentally bypassed by a return, continue, or break. Putting cleanup code in a finally block is always a good practice, even when no exceptions are anticipated.

finalize() – A method that helps in garbage collection. A method that is invoked before an object is discarded by the garbage collector, allowing it to clean up its state. Should not be used to release non-memory resources like file handles, sockets, database connections etc because Java has only a finite number of these resources and you do not know when the garbage collection is going to kick in to release these non-memory resources through the finalize() method.