没有合适的资源?快使用搜索试试~ 我知道了~
java英语面试题
需积分: 10 3 下载量 96 浏览量
2013-02-04
19:46:19
上传
评论
收藏 146KB PDF 举报
温馨提示
试读
17页
java英语面试题
资源推荐
资源详情
资源评论
What is Polymorphism?
The Polymorphism can be referred as one name many forms. It is the ability of methods to behave
differently, depending upon the object who is calling it. The key features of Polymorphism are:
• Allows using one interface for multiple implementations.
• Supports Method Overloading: Multiple methods with same name, but different formal
argument.
• Supports Method Overridden: Multiple methods have the same name, same return type, and
same formal argument list.
Explain garbage collection.
The Java uses the garbage collection to free the memory. By cleaning those objects that is no longer
reference by any of the program. Step involve in cleaning up the garbage collection:
• Garbage Object Collection: first step is to collection and group all those object which are no
more reference with any of the program. We can use the different methods to collect the
garbage object like using runtime.gc() or system.gc().
• Run Finalize method: To free up those object which is collected by the garbage collector java
must execute the Finalize method to delete all those dynamically created object
What is an immutable object?
An immutable object is one that we cannot change once it is created. Steps involved in creation of an
immutable object are:
• Make all of its data fields private.
• Methods which can perform changes in any of the data fields after the construction of object
must be avoided.
How are this() and super() used with constructors?
this() Constructors: is used to pointing the current class instance.
• Can be used with variables or methods.
• Used to call constructer of same class.
• Private variable cannot be accessed using this().
super() Constructer: is used to call constructor of parent class.
• Must be the first statement in the body of constructor.
• Using this we can access private variables in the super class.
What are Access Specifiers available in Java?
Java offers four access specifiers, described below:
• Public: public classes, methods, and fields can be accessed by every class.
• Protected: protected methods and fields can only be accessed within the same class to which
the methods and fields belong.
• Default (no specifier): when we do not set access to specific level, then such a class, method,
or field will be accessible from inside the same package to which the class, method, or field
belongs.
• Private: private methods and fields can only be accessed within the same class to which the
methods and fields belong. Private methods and fields are not inherited by subclasses.
What is Constructor?
A constructor is used to initialize a newly created object.
• It is called just after the memory is allocated for the object.
• It can be used to initialize the objects.
• It is not mandatory to write a constructor for the class.
• Name of constructor is same as the class name.
• Cannot be inherited.
• Constructor is invoked whenever an object of its associated class is created.
What are the List interface and its main implementation?
The List helps in collections of objects. Lists may contain duplicate elements. The main implementations
of the List interface are as follows:
• ArrayList: Resizable-array implementation of the List interface.
• Vector: Synchronized resizable-array implementation of the List.
• LinkedList: Doubly-linked list implementation of the List interface. Better performance than the
ArrayList implementation when elements are inserted or deleted timely.
Explain the user defined Exceptions.
User Defined Exceptions are exceptions defined by the user for specific purposed. This allows custom
exceptions to be generated and caught in the same way as normal exceptions. While defining a User
Defined Exception, we need to take care of the following aspects:
• It should be extend from Exception class.
• Use toString() method to display information about the exception.
Describe life cycle of thread.
Threads follow the single flow of control. A thread is execution in a program. The life cycles of threads are
listed below:
• Newborn state: After the creations of Thread instance the thread is in this state but before the
start() method invocation. Thread is considered not alive in this phase.
• Runnable state: A thread starts its life from Runnable state. After the invoking of start() method
thread enters Runnable state.
• Running state: A thread first enters Runnable state.
• Blocked state: A thread can enter in this state because of waiting the resources that are hold
by another thread.
• Dead state: A thread can be considered dead when its run() method completes. If any thread
comes on this state that means it cannot ever run again.
What is an Applets?
Applets: These are small java programs.
• They can send from one computer to another computer over the internet using the Applet
Viewer that supports java.
• Applets can runs in a Web browser as it is a java program. It can be a fully functional Java
application because it has the entire Java API at its disposal.
• Applets follow the security rules given by the Web browser.
• Applet security is also known as sandbox security.
What is the Set interface?
A Set interface is collection of element which cannot be duplicated.
• The Set interface contains methods inherited from collection.
• It provides methods to access the elements of a finite mathematical set.
• Two Set objects are equal if they contain the same elements.
• It models the mathematical set abstraction.
What is a HashSet and TreeSet?
The HashSet is an unsorted, unordered Set.
• It is Collection set that restrict duplicate elements and also repositioning of elements.
• It implements the Set interface and extends AbstractSet.
• Uses hash code of the object being inserted.
The TreeSet is a Set implemented when we want elements in a sorted order.
• Sorting of element is done according to the natural order of elements or by the help of
comparator provided at creation time.
How do you decide when to use HashMap and when to use TreeMap and what
is difference between these two?
HashMap is used when we want to perform insertion, deletion, and locate elements in a Map.
TreeMap is used when we want to traverse the elements in a sorted order. Depending upon the size of
collection, adding elements to HashMap is easy. For sorted elements traversal we can convert the
HashMAp into TreeMap.
HashMap:
• Lets us to have null values and also one null key
• Iterator in the HashMap is Fail-Safe.
• It is Unsynchronized.
HashTable:
• It does not allow null value as key and value.
• It is not synchronized.
What is the Comparable interface?
The Comparable interface is used to sort collections and arrays of objects using the collections.sort() and
java.utils. The objects of the class implementing the Comparable interface can be ordered. All classes
implementing the Comparable interface must implement the compareTo() method that has the return
type as an integer. The signature of the compareTo() method is as follows:
int i = object1.compareTo(object2)
• If object1 < object2: The value of i returned will be negative.
• If object1 > object2: The value of i returned will be positive.
• If object1 = object2: The value of i returned will be zero.
When should I use abstract classes and when should I use interfaces?
Use Interface, when:
• Design changing frequently or when various implementations only share method signatures.
• We need some classes to use some methods which we do not want to be included in the class.
Use Abstract Class, when:
剩余16页未读,继续阅读
资源评论
xujiewei
- 粉丝: 0
- 资源: 1
上传资源 快速赚钱
- 我的内容管理 展开
- 我的资源 快来上传第一个资源
- 我的收益 登录查看自己的收益
- 我的积分 登录查看自己的积分
- 我的C币 登录后查看C币余额
- 我的收藏
- 我的下载
- 下载帮助
安全验证
文档复制为VIP权益,开通VIP直接复制
信息提交成功