NavigableSet in Java 6.0

NavigableSet API is included in the SCJP 6.0 certification exam. This article explains few important methods with simple example program. NavigableSet is the subinterface of SortedSet. This interface defines methods for finding the element in a list. For example lower() method used for finding the element which is less than the given value. Look into the following example:

package NavigableTutorial.net;

import java.util.ArrayList;
import java.util.List;
import java.util.NavigableSet;
import java.util.TreeSet;

public class NavigableSetTutorial1 {
    public static void main(String args[]){
        List list = new ArrayList();
        list.add(3);
        list.add(4);
        list.add(1);
        list.add(8);
        list.add(7);
        list.add(10);
       
        NavigableSet navigableSet = new TreeSet(list);
        System.out.println(navigableSet.lower(8));
        System.out.println(navigableSet.higher(8));
       
    }
}


Output:
7
10

In the above code, NavigableSet.lower() method is used for reteriving the value which is less than '8' in the list. Same way NavigableSet.higher() is used for reteriving the value greater than '8' in the list.

Java 6 - NavigableSet -headSet and tailSet Example Java Collections Framework

The below example explains the headSet and tailSet methods of the NavigableSet.

package examples;

import java.util.NavigableSet;
import java.util.TreeSet;
public class NavigableSetExample {

public static void main(String[] args) {
NavigableSet set = new TreeSet();
// Add elements in to the Navigable Set
set.add(1);
set.add(2);
set.add(3);
System.out.println(set);

// Head Set
System.out.println("Head Set :" + set.headSet(2));
System.out.println("Head Set including given integer: "+ set.headSet(2, true));

// Tail Set
System.out.println("Tail Set" + set.tailSet(2));
System.out.println("Tail Set including given integer: " + set.tailSet(2, false));
}

}

[1, 2, 3]
Head Set :[1]
Head Set including given integer: [1, 2]
Tail Set[2, 3]
Tail Set including given integer: [3]

NavigableSet - pollFirst and pollLast example Java Collections

pollFirst(), pollLast() methods of NavigableSet can be used to remove first and last element of the Set respectively. The below program explains the pollFirst() and pollLast()


package examples;

import java.util.NavigableSet;
import java.util.TreeSet;

public class NavigableSetExample {

public static void main(String args[]){
NavigableSet navigableSet = new TreeSet();

navigableSet.add(1);
navigableSet.add(2);

System.out.println("Set : " + navigableSet);

navigableSet.pollFirst();

System.out.println("Set After pollFirst " + navigableSet);

navigableSet.add(3);
navigableSet.add(4);

System.out.println("Set " + navigableSet);

navigableSet.pollLast();

System.out.println("Set after pollLast " +navigableSet);

}

}

Output:

Set : [1, 2]
Set After pollFirst [2]
Set [2, 3, 4]
Set after pollLast [2, 3]

Java Collections Tutorial Navigable Map Example

package JAVATUTORIAL;
import java.util.*;
import java.util.concurrent.*;

public class NavigableMapTutorial{
      public static void main(String[] args) {
        System.out.println("Navigable Map Example!\n");
        NavigableMap navMapObj = new
                           ConcurrentSkipListMap();
        navMapObj.put(1, "S");
        navMapObj.put(2, "February");
        navMapObj.put(3, "March");
        navMapObj.put(4, "April");
        navMapObj.put(5, "May");
        navMapObj.put(6, "June");
        navMapObj.put(7, "July");
        navMapObj.put(8, "August");
        navMapObj.put(9, "September");
        navMapObj.put(10, "October");
        navMapObj.put(11, "November");
        navMapObj.put(12, "December");
        //Displaying all data
        System.out.println("Data in Navigable Map is : " +
                                              navMapObj.descendingMap()+"\n");
        //Retrieving first data
        System.out.print("First data: " + navMapObj.firstEntry()+"\n");
        //Retrieving last data
        System.out.print("Last data: " + navMapObj.lastEntry()+"\n\n");
        //Retrieving the nreatest less than or equal to the given key
        System.out.print("Nearest less than or equal to the given key: "
                                + navMapObj.floorEntry(5)+"\n");
        //Retrieving the greatest key strictly less than the given key
        System.out.println("Retrieving the greatest key strictly less than the given key"+ navMapObj.lowerEntry(3));
        //Retrieving a key-value associated with the least key
                        //strictly greater than the given key
        System.out.println("Retriving data from navigable map greter than   the given key: " + navMapObj.higherEntry(5)+"\n");
        //Removing first
        System.out.println("Removing First: " + navMapObj.pollFirstEntry());
        //Removing last
        System.out.println("Removing Last: " + navMapObj.pollLastEntry()+"\n");
        //Displaying all data
        System.out.println("Now data: " + navMapObj.descendingMap());
      }
    }
     

Description of program:

The following program helps you in inserting, removing and retrieving the data from the NavigableMap. It uses the put() method to add the element. If you want to retrieve the data at first and last position from the NavigableMap, you use the firstEntry() and lastEntry() methods. The descendingMap() method represents all data to the NavigableMap in descending order.

You can retrieve the nearest less than or equal to the given number and the greatest key strictly less than the given number floorEntry() and lowerEntry() methods. And you retrieve a key-value associated with the least key strictly greater than the given key, you use the higherEntry() method. The pollFirstEntry() method removes the first data from the NavigableMap and pollLastEntry() method also removes the data at the last position from the NavigableMap.

JDK 6 Collections-related APIs & Developer Guides |Java 6.0 Collection Framework

Java 6.0 New Collection APIs an Overview
The following are the new collection APIs introduced in Java 6.0. I listes them as Interfaces and classes.
New Interfaces

• Deque
• BlockingDeque
• NavigableSet
• NavigableMap

New Classes

• ArrayDeque
• LinkedBlockingDeque
• ConcurrentSkipListSet
• ConcurrentSkipListMap
• AbstractMap.SimpleEntry
• AbstractMap.SimpleImmutableEntry

Updated Classes in Java 6.0

• LinkedList
• TreeSet
• TreeMap
• Collections

Advantages and Disadvantages of the Java Collection Framework

A collection is simply an object that groups multiple elements into a single unit. It is also called as a container sometimes. It is used to store, retrieve, manipulate, and communicate aggregate data. Typically, it represents data items that form a natural group and allows duplicate elements while others do not. It consists of both ordered and unordered elements. 

The primary advantages of a collections framework are that it:

Reduces programming effort by providing useful data structures and algorithms so you don't have to write them yourself.
Increases performance by providing high-performance implementations of useful data structures and algorithms. Because the various implementations of each interface are interchangeable, programs can be easily tuned by switching implementations.
Provides interoperability between unrelated APIs by establishing a common language to pass collections back and forth.
Reduces the effort required to learn APIs by eliminating the need to learn multiple ad hoc collection APIs.
Reduces the effort required to design and implement APIs by eliminating the need to produce ad hoc collections APIs.
Fosters software reuse by providing a standard interface for collections and algorithms to manipulate them.

Disadvantages of collections framework:

It must cast to correct type.
It can't be done compile-time type checking.

What is Collection Framework in Java?

A collection is an object that represents a group of objects (such as the familiar Vector class). A collections framework is a unified architecture for representing and manipulating collections, allowing them to be manipulated independently of the details of their representation.

collections is a group of objects known as its elements. Basically it is a package of data structures that includes ArrayLists, LinkedLists, HashSets, etc. A collection is simply an object that groups multiple elements into a single unit. It is also called as a container sometimes. It is used to store, retrieve, manipulate, and communicate aggregate data. Typically, it represents data items that form a natural group and allows duplicate elements while others do not. It consists of both ordered and unordered elements. There is no direct implementation of this interface however SDK provides implementations of more specific sub interfaces like Set and List. The manipulation and passing of collections is done by this interface.

Java interview questions & answers -Set 2

• What is meant by Inheritance and what are its advantages?- Inheritance is the process of inheriting all the features from a class. The advantages of inheritance are reusability of code and accessibility of variables and methods of the super class by subclasses.
• What is the difference between this() and super()?- this() can be used to invoke a constructor of the same class whereas super() can be used to invoke a super class constructor.
• What is the difference between superclass and subclass?- A super class is a class that is inherited whereas sub class is a class that does the inheriting.
• What modifiers may be used with top-level class?- public, abstract and final can be used for top-level class.
• What are inner class and anonymous class?- Inner class : classes defined in other classes, including those defined in methods are called inner classes. An inner class can have any accessibility including private. Anonymous class : Anonymous class is a class defined inside a method without a name and is instantiated and declared in the same place and cannot have explicit constructors.
• What is a package?- A package is a collection of classes and interfaces that provides a high-level layer of access protection and name space management.
• What is a reflection package?- java. lang. reflect package has the ability to analyze itself in runtime.
• What is interface and its use?- Interface is similar to a class which may contain method’s signature only but not bodies and it is a formal set of method and constant declarations that must be defined by the class that implements it. Interfaces are useful for: a)Declaring methods that one or more classes are expected to implement b)Capturing similarities between unrelated classes without forcing a class relationship. c)Determining an object’s programming interface without revealing the actual body of the class.
• What is an abstract class?- An abstract class is a class designed with implementation gaps for subclasses to fill in and is deliberately incomplete.
• What is the difference between Integer and int?- a) Integer is a class defined in the java. lang package, whereas int is a primitive data type defined in the Java language itself. Java does not automatically convert from one to the other. b) Integer can be used as an argument for a method that requires an object, whereas int can be used for calculations.
• What is a cloneable interface and how many methods does it contain?- It is not having any method because it is a TAGGED or MARKER interface.
• What is the difference between abstract class and interface?- a) All the methods declared inside an interface are abstract whereas abstract class must have at least one abstract method and others may be concrete or abstract. b) In abstract class, key word abstract must be used for the methods whereas interface we need not use that keyword for the methods. c) Abstract class must have subclasses whereas interface can’t have subclasses.
• Can you have an inner class inside a method and what variables can you access?- Yes, we can have an inner class inside a method and final variables can be accessed.
• What is the difference between String and String Buffer?- a) String objects are constants and immutable whereas StringBuffer objects are not. b) String class supports constant strings whereas StringBuffer class supports growable and modifiable strings.
• What is the difference between Array and vector?- Array is a set of related data type and static whereas vector is a growable array of objects and dynamic.
• What is the difference between exception and error?- The exception class defines mild error conditions that your program encounters. Exceptions can occur when trying to open the file, which does not exist, the network connection is disrupted, operands being manipulated are out of prescribed ranges, the class file you are interested in loading is missing. The error class defines serious error conditions that you should not attempt to recover from. In most cases it is advisable to let the program terminate when such an error is encountered.
• What is the difference between process and thread?- Process is a program in execution whereas thread is a separate path of execution in a program.
• What is multithreading and what are the methods for inter-thread communication and what is the class in which these methods are defined?- Multithreading is the mechanism in which more than one thread run independent of each other within the process. wait (), notify () and notifyAll() methods can be used for inter-thread communication and these methods are in Object class. wait() : When a thread executes a call to wait() method, it surrenders the object lock and enters into a waiting state. notify() or notifyAll() : To remove a thread from the waiting state, some other thread must make a call to notify() or notifyAll() method on the same object.
• What is the class and interface in java to create thread and which is the most advantageous method?- Thread class and Runnable interface can be used to create threads and using Runnable interface is the most advantageous method to create threads because we need not extend thread class here.
• What are the states associated in the thread?- Thread contains ready, running, waiting and dead states.

How to Convert Exponential Form of a number to Decimal Form in java

In Java you will see that most of the value are displayed in Exponential form while using Doubles and Long.


Example:
In following we are multiplying 4.58 with 10000 and the result is printed.

Double a = 4.58d / 10000; System.out.println( a.doubleValue());   a = 2.85d * 100000000; System.out.println( a.doubleValue());

Result:

4.58E-4
 4.58E8

You can do this simply by using class java.math.BigDecimal. In following example we are using BigDecimal.valueOf() to convert the Double value to BigDecimal and than .toPlainString() to convert it into plain decimal string.

import java.math.BigDecimal; Double a = 4.58d / 10000; System.out.println(BigDecimal.valueOf(a).toPlainString());  a = 4.58d * 100000000; System.out.println(BigDecimal.valueOf(a).toPlainString());

Result:
0.000458 

458000000

What is the difference between an Interface and an Abstract class?

An Abstract Class can contain default Implementation, where as an Interface should not contain any implementation at all. An Interface should contain only definitions but no implementation. where as an abstract class can contain abstract and non-abstract methods. When a class inherits from an abstract, the derived class must implement all the abstract methods declared in the base class. an abstract class can inherit from another non-abstract class.

Comparision Table

Abstract classes	Interfaces
Abstract classes are used only when there is a “is-a” type of relationship between the classes.	Interfaces can be implemented by classes that are not related to one another.
You cannot extend more than one abstract class.	You can implement more than one interface.
Abstract class can implemented some methods also.	Interfaces can not implement methods.
With abstract classes, you are grabbing away each class’s individuality.	With Interfaces, you are merely extending each class’s functionality.