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Android interview questions #Nitin #Tekale
Android interview questions : Interview preparation for android development : Important question answer in Android
Hello Friends, Some important question for Interview in Android.....
What is android?
Android is a stack of software for mobile devices which has Operating System, middleware and some key
applications. The application executes within its own process and its own instance of Dalvik Virtual Machine.
Many Virtual Machines run efficiently by a DVM device. DVM executes Java languages byte code which later
transforms into .dex format files.
What is activity?
A single screen in an application, with supporting Java code.
What is intent in Android?
A class (Intent) will describes what a caller desires to do. The caller will send this intent to Android's intent
resolver, which finds the most suitable activity for the intent. E.g. opening a PDF document is an intent, and
the Adobe Reader apps will be the perfect activity for that intent(class).
What is a Sticky Intent?
sendStickyBroadcast() performs a sendBroadcast (Intent) known as sticky, i.e. the Intent you are sending
stays around after the broadcast is complete, so that others can quickly retrieve that data through the
return value of registerReceiver (BroadcastReceiver, IntentFilter). In all other ways, this behaves the same
as sendBroadcast(Intent).
One example of a sticky broadcast sent via the operating system is ACTION_BATTERY_CHANGED.
When you call registerReceiver() for that action -- even with a null BroadcastReceiver -- you get the
Intent that was last broadcast for that action. Hence, you can use this to find the state of the battery
without necessarily registering for all future state changes in the battery.
Is there anyway to determine if an Intent passed into a BroadcastReceiver's onReceive is the result
of a sticky Boradcast Intent, or if it was just sent?
Example for sticky broadcast
When you call registerReceiver() for that action -- even with a null BroadcastReceiver -- you get
the Intent that was last broadcast for that action. Hence, you can use this to find the state of
the battery without necessarily registering for all future state changes in the battery.
How the nine-patch Image different from a regular bitmap? or Different between
nine-patch Image vs regular Bitmap Image
It is one of a resizable bitmap resource which is being used as backgrounds or other images on the device.
The NinePatch class allows drawing a bitmap in nine sections. The four corners are unscaled; the middle
of the image is scaled in both axes, the four edges are scaled into one axis.
What Programming languages does Android support for application development?
Android applications supports using Java Programming Language. which is coded in Java and
complied using Android SDK.
What is a resource?
A user defined JSON, XML, bitmap, or other file, injected into the application build process,
which can later be loaded from code.
How will you record a phone call in Android? or How to handle on Audio Stream for a call in Android?
Permissions.PROCESS_OUTGOING_CALLS: Will Allows an application to monitor, modify, or abort
outgoing calls. So through that we can monitor the Phone calls.
What's the difference between class, file and activity in android?
Class - The Class file is complied from .java file. Android will use this .class file to produce the executable apk.
File - It is a block of resources, srbitrary information. It can be any file type.
Activity - An activity is the equivalent of a Frame/Window in GUI toolkits. It is not a file or a file
type it is just a class that can be extended in Android for loading UI elements on view.
What is APK format?
The APK file is compressed AndroidManifest.xml file with extension .apk, Which have application code
(.dex files), resource files, and other files which is compressed into single .apk file.
How to Translate in android?
The Google translator translates the data of one language into another language by using
XMPP to transmit data. You can type the message in English and select the language which is
understood by the citizens of the country in order to reach the message to the citizens.
What is an action?
A description of something that an Intent sender desires.
What are the advantages of Android?
The following are the advantages of Android:
* The customer will be benefited from wide range of mobile applications to choose, since the monopoly
of wireless carriers like Orange and AT&T will be broken by Google Android.
* Features like weather details, live RSS feeds, opening screen, icon on the opening screen can be customized
* Innovative products like the location-aware services, location of a nearby convenience store etc.,
are some of the additive facilities in Android.
What is the TTL (Time to Live)? Why is it required?
TTL is a value in data packet of Internet Protocol. It communicates to the network router whether or not
the packet should be in the network for too long or discarded. Usually, data packets might not be transmitted
to their intended destination within a stipulated period of time. The TTL value is set by a system default
value which is an 8-bit binary digit field in the header of the packet. The purpose of TTL is, it would specify
certain time limit in seconds, for transmitting the packet header. When the time is exhausted, the packet
would be discarded. Each router receives the subtracts count, when the packet is discarded, and when it
becomes zero, the router detects the discarded packets and sends a message, Internet Control Message
Protocol message back to the originating host.
How is nine-patch image different from a regular bitmap?
It is a resizable bitmap resource that can be used for backgrounds or other images on the device.
The NinePatch class permits drawing a bitmap in nine sections. The four corners are unscaled; the four
edges are scaled in one axis, and the middle is scaled in both axes.
Explain IP datagram, Fragmentation and MTU ?
IP datagram can be used to describe a portion of IP data. Each IP datagram has set of fields arranged in an
order. The order is specific which helps to decode and read the stream easily. IP datagram has fields like
Version, header length, Type of service, Total length, checksum, flag, protocol, Time to live, Identification,
source and destination ip address, padding, options and payload.
MTU:- Maximum Transmission Unit is the size of the largest packet that a communication protocol can pass.
The size can be fixed by some standard or decided at the time of connection
Fragmentation is a process of breaking the IP packets into smaller pieces. Fragmentation is needed when
the datagram is larger than the MTU. Each fragment becomes a datagram in itself and transmitted
independently from source. When received by destination they are reassembled.
Explain about the exceptions of Android?
The following are the exceptions that are supported by Android
* InflateException : When an error conditions are occurred, this exception is thrown
* Surface.OutOfResourceException: When a surface is not created or resized, this exception is thrown
* SurfaceHolder.BadSurfaceTypeException: This exception is thrown from the lockCanvas() method, when
invoked on a Surface whose is SURFACE_TYPE_PUSH_BUFFERS
* WindowManager.BadTokenException: This exception is thrown at the time of trying to add view an invalid
WindowManager.LayoutParamstoken.
Describe Android Application Architecture?
Android Application Architecture has the following components:
* Services ? like Network Operation
* Intent - To perform inter-communication between activities or services
* Resource Externalization - such as strings and graphics
* Notification signaling users - light, sound, icon, notification, dialog etc.
* Content Providers - They share data between applications
Explain about the exceptions of Android?
The following are the exceptions that are supported by Android
* InflateException : When an error conditions are occurred, this exception is thrown
* Surface.OutOfResourceException: When a surface is not created or resized, this exception is thrown
* SurfaceHolder.BadSurfaceTypeException: This exception is thrown from the lockCanvas() method,
when invoked on a Surface whose is SURFACE_TYPE_PUSH_BUFFERS
* WindowManager.BadTokenException: This exception is thrown at the time of trying to add view
an invalid WindowManager.LayoutParamstoken.
What are the features of Android?
*Components can be reused and replaced by the application framework.
*Optimized DVM for mobile devices
*SQLite enables to store the data in a structured manner.
*Supports GSM telephone and Bluetooth, WiFi, 3G and EDGE technologies
*The development is a combination of a device emulator, debugging tools, memory profiling and plug-in for
Eclipse IDE.
What are the differences between a domain and a workgroup?
In a domain, one or more computer can be a server to manage the network. On the other hand in a
workgroup all computers are peers having no control on each other. In a domain, user doesn?t need an
account to logon on a specific computer if an account is available on the domain. In a work group user
needs to have an account for every computer.
In a domain, Computers can be on different local networks. In a work group all computers needs to be
a part of the same local network.
What is needed to make a multiple choice list with a custom view for each row?
Multiple choice list can be viewed by making the CheckBox android:id value be “@android:id /text1".
That is the ID used by Android for the CheckedTextView in simple_list_item_multiple_choice.
What are the dialog boxes that are supported in android? Explain.
Android supports 4 dialog boxes:
AlertDialog : An alert dialog box supports 0 to 3 buttons and a list of selectable elements, including check
boxes and radio buttons. Among the other dialog boxes, the most suggested dialog box is the alert dialog box.
ProgressDialog: This dialog box displays a progress wheel or a progress bar. It is an extension of AlertDialog
and supports adding buttons.
DatePickerDialog: This dialog box is used for selecting a date by the user.
TimePickerDialog: This dialog box is used for selecting time by the user.
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#Nitin #Tekale Java Interview Question Answer #Nitin #Tekale
Java Inerview
Java Interview Question Answer:
Java was developed by a team of computer professionals under the guidance of James
Gosling at Sun Microsystems in 1991. They wanted to give a suitable name. Initially
they called it “oak” after seeing an oak tree from their window, but after some weeks
they were discussing another name and were sipping Java coffee, so one of them
suggested the name “Java”.
Q: What is the difference between an Interface and an Abstract class?
A: An abstract class can have instance methods that implement a default behavior. An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract. An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.
Q: What is the purpose of garbage collection in Java, and when is it used?
A: The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used.
Q: Describe synchronization in respect to multithreading.
A: With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchonization, it is possible for one thread to modify a shared variable while another thread is in the process of using or updating same shared variable. This usually leads to significant errors.
Q: Explain different way of using thread?
Q: Describe synchronization in respect to multithreading.
A: With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchonization, it is possible for one thread to modify a shared variable while another thread is in the process of using or updating same shared variable. This usually leads to significant errors.
Q: Explain different way of using thread?
A: The thread could be implemented by using runnable interface or by inheriting from the Thread class. The former is more advantageous, 'cause when you are going for multiple inheritance..the only interface can help.
Q: What are pass by reference and passby value?
A: Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.
Q: What is HashMap and Map?
A: Map is Interface and Hashmap is class that implements that.
Q: Difference between HashMap and HashTable?
A: The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesnt allow). HashMap does not guarantee that the order of the map will remain constant over time. HashMap is unsynchronized and Hashtable is synchronized.
Q: Difference between Vector and ArrayList?
A: Vector is synchronized whereas arraylist is not.
Q: Difference between Swing and Awt?
A: AWT are heavy-weight componenets. Swings are light-weight components. Hence swing works faster than AWT.
Q: What is the difference between a constructor and a method?
A: A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator.
A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.
Q: What is an Iterator?
A: Some of the collection classes provide traversal of their contents via a java.util.Iterator interface. This interface allows you to walk through a collection of objects, operating on each object in turn. Remember when using Iterators that they contain a snapshot of the collection at the time the Iterator was obtained; generally it is not advisable to modify the collection itself while traversing an Iterator.
Q: What are pass by reference and passby value?
A: Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.
Q: What is HashMap and Map?
A: Map is Interface and Hashmap is class that implements that.
Q: Difference between HashMap and HashTable?
A: The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesnt allow). HashMap does not guarantee that the order of the map will remain constant over time. HashMap is unsynchronized and Hashtable is synchronized.
Q: Difference between Vector and ArrayList?
A: Vector is synchronized whereas arraylist is not.
Q: Difference between Swing and Awt?
A: AWT are heavy-weight componenets. Swings are light-weight components. Hence swing works faster than AWT.
Q: What is the difference between a constructor and a method?
A: A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator.
A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.
Q: What is an Iterator?
A: Some of the collection classes provide traversal of their contents via a java.util.Iterator interface. This interface allows you to walk through a collection of objects, operating on each object in turn. Remember when using Iterators that they contain a snapshot of the collection at the time the Iterator was obtained; generally it is not advisable to modify the collection itself while traversing an Iterator.
Q: State the significance of public, private, protected, default modifiers both singly and in combination and state the effect of package relationships on declared items qualified by these modifiers.
A: public : Public class is visible in other packages, field is visible everywhere (class must be public too)
private : Private variables or methods may be used only by an instance of the same class that declares the variable or method, A private feature may only be accessed by the class that owns the feature.
protected : Is available to all classes in the same package and also available to all subclasses of the class that owns the protected feature.This access is provided even to subclasses that reside in a different package from the class that owns the protected feature.
default :What you get by default ie, without any access modifier (ie, public private or protected).It means that it is visible to all within a particular package.
Q: What is an abstract class?
A: Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that is abstract may not be instantiated (ie, you may not call its constructor), abstract class may contain static data. Any class with an abstract method is automatically abstract itself, and must be declared as such.
A class may be declared abstract even if it has no abstract methods. This prevents it from being instantiated.
Q: What is static in java?
A: Static means one per class, not one for each object no matter how many instance of a class might exist. This means that you can use them without creating an instance of a class.Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can't override a static method with a nonstatic method. In other words, you can't change a static method into an instance method in a subclass.
Q: What is final?
A: A final class can't be extended ie., final class may not be subclassed. A final method can't be overridden when its class is inherited. You can't change value of a final variable (is a constant).
A: public : Public class is visible in other packages, field is visible everywhere (class must be public too)
private : Private variables or methods may be used only by an instance of the same class that declares the variable or method, A private feature may only be accessed by the class that owns the feature.
protected : Is available to all classes in the same package and also available to all subclasses of the class that owns the protected feature.This access is provided even to subclasses that reside in a different package from the class that owns the protected feature.
default :What you get by default ie, without any access modifier (ie, public private or protected).It means that it is visible to all within a particular package.
Q: What is an abstract class?
A: Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that is abstract may not be instantiated (ie, you may not call its constructor), abstract class may contain static data. Any class with an abstract method is automatically abstract itself, and must be declared as such.
A class may be declared abstract even if it has no abstract methods. This prevents it from being instantiated.
Q: What is static in java?
A: Static means one per class, not one for each object no matter how many instance of a class might exist. This means that you can use them without creating an instance of a class.Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can't override a static method with a nonstatic method. In other words, you can't change a static method into an instance method in a subclass.
Q: What is final?
A: A final class can't be extended ie., final class may not be subclassed. A final method can't be overridden when its class is inherited. You can't change value of a final variable (is a constant).
Q: What if the main method is declared as private?
A: The program compiles properly but at runtime it will give "Main method not public." message.
Q: What if the static modifier is removed from the signature of the main method?
A: Program compiles. But at runtime throws an error "NoSuchMethodError".
Q: What if I write static public void instead of public static void?
A: Program compiles and runs properly.
Q: What if I do not provide the String array as the argument to the method?
A: Program compiles but throws a runtime error "NoSuchMethodError".
Q: What is the first argument of the String array in main method?
A: The String array is empty. It does not have any element. This is unlike C/C++ where the first element by default is the program name.
Q: If I do not provide any arguments on the command line, then the String array of Main method will be empty or null?
A: It is empty. But not null.
Q: How can one prove that the array is not null but empty using one line of code?
A: Print args.length. It will print 0. That means it is empty. But if it would have been null then it would have thrown a NullPointerException on attempting to print args.length.
Q: What environment variables do I need to set on my machine in order to be able to run Java programs?
A: CLASSPATH and PATH are the two variables.
Q: Can an application have multiple classes having main method?
A: Yes it is possible. While starting the application we mention the class name to be run. The JVM will look for the Main method only in the class whose name you have mentioned. Hence there is not conflict amongst the multiple classes having main method.
Q: Can I have multiple main methods in the same class?
A: No the program fails to compile. The compiler says that the main method is already defined in the class.
Q: What if the static modifier is removed from the signature of the main method?
A: Program compiles. But at runtime throws an error "NoSuchMethodError".
Q: What if I write static public void instead of public static void?
A: Program compiles and runs properly.
Q: What if I do not provide the String array as the argument to the method?
A: Program compiles but throws a runtime error "NoSuchMethodError".
Q: What is the first argument of the String array in main method?
A: The String array is empty. It does not have any element. This is unlike C/C++ where the first element by default is the program name.
Q: If I do not provide any arguments on the command line, then the String array of Main method will be empty or null?
A: It is empty. But not null.
Q: How can one prove that the array is not null but empty using one line of code?
A: Print args.length. It will print 0. That means it is empty. But if it would have been null then it would have thrown a NullPointerException on attempting to print args.length.
Q: What environment variables do I need to set on my machine in order to be able to run Java programs?
A: CLASSPATH and PATH are the two variables.
Q: Can an application have multiple classes having main method?
A: Yes it is possible. While starting the application we mention the class name to be run. The JVM will look for the Main method only in the class whose name you have mentioned. Hence there is not conflict amongst the multiple classes having main method.
Q: Can I have multiple main methods in the same class?
A: No the program fails to compile. The compiler says that the main method is already defined in the class.
Q: Do I need to import java.lang package any time? Why ?
A: No. It is by default loaded internally by the JVM.
Q: Can I import same package/class twice? Will the JVM load the package twice at runtime?
A: One can import the same package or same class multiple times. Neither compiler nor JVM complains abt it. And the JVM will internally load the class only once no matter how many times you import the same class.
Q: What are Checked and UnChecked Exception?
A: A checked exception is some subclass of Exception (or Exception itself), excluding class RuntimeException and its subclasses.
Making an exception checked forces client programmers to deal with the possibility that the exception will be thrown. eg, IOException thrown by java.io.FileInputStream's read() method·
Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and its subclasses also are unchecked. With an unchecked exception, however, the compiler doesn't force client programmers either to catch the
exception or declare it in a throws clause. In fact, client programmers may not even know that the exception could be thrown. eg, StringIndexOutOfBoundsException thrown by String's charAt() method· Checked exceptions must be caught at compile time. Runtime exceptions do not need to be. Errors often cannot be.
Q: What is Overriding?
A: When a class defines a method using the same name, return type, and arguments as a method in its superclass, the method in the class overrides the method in the superclass.
When the method is invoked for an object of the class, it is the new definition of the method that is called, and not the method definition from superclass. Methods may be overridden to be more public, not more private.
Q: What are different types of inner classes?
A: Nested top-level classes, Member classes, Local classes, Anonymous classes
Nested top-level classes- If you declare a class within a class and specify the static modifier, the compiler treats the class just like any other top-level class.
A: No. It is by default loaded internally by the JVM.
Q: Can I import same package/class twice? Will the JVM load the package twice at runtime?
A: One can import the same package or same class multiple times. Neither compiler nor JVM complains abt it. And the JVM will internally load the class only once no matter how many times you import the same class.
Q: What are Checked and UnChecked Exception?
A: A checked exception is some subclass of Exception (or Exception itself), excluding class RuntimeException and its subclasses.
Making an exception checked forces client programmers to deal with the possibility that the exception will be thrown. eg, IOException thrown by java.io.FileInputStream's read() method·
Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and its subclasses also are unchecked. With an unchecked exception, however, the compiler doesn't force client programmers either to catch the
exception or declare it in a throws clause. In fact, client programmers may not even know that the exception could be thrown. eg, StringIndexOutOfBoundsException thrown by String's charAt() method· Checked exceptions must be caught at compile time. Runtime exceptions do not need to be. Errors often cannot be.
Q: What is Overriding?
A: When a class defines a method using the same name, return type, and arguments as a method in its superclass, the method in the class overrides the method in the superclass.
When the method is invoked for an object of the class, it is the new definition of the method that is called, and not the method definition from superclass. Methods may be overridden to be more public, not more private.
Q: What are different types of inner classes?
A: Nested top-level classes, Member classes, Local classes, Anonymous classes
Nested top-level classes- If you declare a class within a class and specify the static modifier, the compiler treats the class just like any other top-level class.
Any class outside the declaring class accesses the nested class with the declaring class name acting similarly to a package. eg, outer.inner. Top-level inner classes implicitly have access only to static variables.There can also be inner interfaces. All of these are of the nested top-level variety.
Member classes - Member inner classes are just like other member methods and member variables and access to the member class is restricted, just like methods and variables. This means a public member class acts similarly to a nested top-level class. The primary difference between member classes and nested top-level classes is that member classes have access to the specific instance of the enclosing class.
Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only within the block of their declaration. In order for the class to be useful beyond the declaration block, it would need to implement a
more publicly available interface.Because local classes are not members, the modifiers public, protected, private, and static are not usable.
Anonymous classes - Anonymous inner classes extend local inner classes one level further. As anonymous classes have no name, you cannot provide a constructor.
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Member classes - Member inner classes are just like other member methods and member variables and access to the member class is restricted, just like methods and variables. This means a public member class acts similarly to a nested top-level class. The primary difference between member classes and nested top-level classes is that member classes have access to the specific instance of the enclosing class.
Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only within the block of their declaration. In order for the class to be useful beyond the declaration block, it would need to implement a
more publicly available interface.Because local classes are not members, the modifiers public, protected, private, and static are not usable.
Anonymous classes - Anonymous inner classes extend local inner classes one level further. As anonymous classes have no name, you cannot provide a constructor.
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