pollLast(): remove & returns last element

7) descendingSet(): returns the NavigationSet in reverse order /**@author:Venu Kumar.S @date:Oct 6, 2012

* @fileName:NavigableSetDemo

.java

*/

import java.util.*;

class NavigableSetDemo {

public static void main(String args[]) {

TreeSet<Integer> t=new TreeSet<Integer>();

t.add(1000);

t.add(2000);

t.add(3000);

t.add(4000);

t.add(5000);

System.out.println("Tree Map" + t);

System.out.println("t.ceiling(2000)= " + t.ceiling(2000));

System.out.println("t.higher(2000)= " + t.higher(2000));

System.out.println("t.floor(3000)= " + t.floor(3000));

System.out.println("t.lower(3000)= " + t.lower(3000));

System.out.println("t.pollFirst()= " + t.pollFirst());

System.out.println("t.pollLast()= " + t.pollLast());

System.out.println("t.descendingSet()= " + t.descendingSet());

System.out.println("Tree Map" + t);

} }

||Om Shree Hanumathe Namaha||

Venu Kumaar.S

/*

OUTPUT: javac NavigableSetDemo

Tree Map[1000, 2000, 3000, 4000, 5000]

t.ceiling(2000)= 2000 t.higher(2000)= 3000 t.floor(3000)= 3000 t.lower(3000)= 2000 t.pollFirst()= 1000 t.pollLast()= 5000

t.descendingSet()= [4000, 3000, 2000]

Tree Map[2000, 3000, 4000]

*/

Hash Set Tree Set Storage method:

→

hash table red black tree Space used:

→

O(n) O(n)

Put speed:

→

O(1) O(lg n) Iteration order:

→

Arbitrary Sorted Hash map Tree map

Storage method:

→

hash table red black tree Space used:

→

O(n) O(n)

Put speed:

→

O(1) O(lg n) Iteration order:

→

Arbitrary Sorted concrete implements description

||Om Shree Hanumathe Namaha||

Venu Kumaar.S collection

HashSet Set hash table

TreeSet SortedSet balanced binary tree ArrayList List resizable-array LinkedList List linked list Vector List resizable-array HashMap Map hash table

TreeMap SortedMap balanced binary tree Hashtable Map hash table

Queue (v1.5)

Queue(I) → PriorityQueue(c)

→ BlockingQueue(c) → PriorityBlockingQueue

→ LinkedBlockingQueue

Queue(I):

→

It is the child Interface of collection. if we want to represent a group of individual objects prior to processing then we should go for Queue.

/**@author:Venu Kumar.S @date:Oct 6, 2012

* @fileName:PriorityQueueDemo

.java

*/

import java.util.*;

import java.io.*;

class PriorityQueueDemo {

public static void main(String[] args) throws IOException { PriorityQueue q = new PriorityQueue();

System.out.println("q.peek() :" + q.peek()); // null

// System.out.println(q.element()); //RE: NoSuchElementException for (int i = 0; i <= 10; i++) {

q.offer(i);

||Om Shree Hanumathe Namaha||

Venu Kumaar.S

}

System.out.println("Priority Q: " + q);

System.out.println("q.poll() :" + q.poll()); // del and returns the head element System.out.println("After Poll Priority Q: " + q);

} }

/*

OUTPUT:

java PriorityQueueDemo q.peek() :null

Priority Q: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

q.poll() :0

After Poll Priority Q: [1, 3, 2, 7, 4, 5, 6, 10, 8, 9]

*/

PriorityQueue(C)

→

PriorityQueue is the DS to hold a group of individual objs prior to processing according to some priority.

→

The priority can be either default natural sorting order or customized sorting order.

→

If we are depending on default natural sorting compulsory objects should be homogeneous &

Comparable otherwise we will get classCastException.

→

If we are defining our own customized sorting by Comparator then the objects need not be Homogeneous and Comparable.

→

Duplicate objs are not allowed.

→

Insertion order is not preserved.

→

null insertion is not possible even as first element also.

/**@author:Venu Kumar.S @date:Oct 6, 2012

* @fileName:PriorityQueueDemo1

.java

*/

import java.util.*;

import java.io.*;

class PriorityQueueDemo1 {

public static void main(String[] args) throws IOException {

PriorityQueue q = new PriorityQueue(15, new MyComparator3());

System.out.println("q.peek() :" + q.peek()); // null

// System.out.println(q.element()); //RE NoSuchElementException q.offer("A");

q.offer("Z");

q.offer("L");

q.offer("B");

||Om Shree Hanumathe Namaha||

Venu Kumaar.S

System.out.println("Priority Q: " + q);

} }

class MyComparator3 implements Comparator { public int compare(Object obj1, Object obj2) {

String s1 = (String) obj1;

String s2 = (String) obj2;

return s2.compareTo(s1);

} }

/*

OUTPUT:

java PriorityQueueDemo1 q.peek() :null

Priority Q: [Z, B, L, A]

*/

Package

Package:

→

It is an Encapsulation mechanism to group related classes and interfaces into a single module. The main purposes of packages are:

1. To resolve naming conflicts.

2. To provide security to the classes & interfaces, so that outside person can't access directly.

3. It improves modularity of the application.

java package

→

lang, io, net, util, awt, applet, sql, rmi, math, text javax package

→

swing, sql, xml, naming, transaction

→

There is one universally accepted convention to name packages i.e., to use internet domain name in reverse.

domain name in reverse.module name.submodule name.class name Ex: com.hdfcbank.loan.housingloan.Account

package com.venu.kumar;

public class TestPackage {

public static void main(String[] args) { System.out.println("Package demo");

} }

1. javac TestPackage.java → Generated class file will be placed in current working directory.

2. javac -d . TestPackage.java

||Om Shree Hanumathe Namaha||

Venu Kumaar.S

-d

→

destination to place generated class files .

→

current working directory

→

Generated class file will be placed into corresponding package structure.

→

If specified package structure is not already available then this command itself will create that package structure.

/**@author:Venu Kumar.S @date:Oct 6, 2012

* @fileName:TestPackage

.java

*/

package com.venu.kumar;

public class TestPackage {

public static void main(String[] args) { System.out.println("Package demo");

} }

/*

To compile:

javac -d . TestPackage.java

→

The generated class file is placed in corresponding package structure

-d

→

destination to place generated class file .

→

current working directory

TestPackage.class is placed in com

→

^venu

→

^kumar

→

TestPackage.class To Execute:

java com.venu.kumar.TestPackage output:

Package demo

*/

static imports:

This feature is introduced in java 5 to import static members of class By using this feature we can access all

→

→

non-private static members without using class name from other classes with in the package and

→

protected and public members from outside package class members without using class name.

syntax: import static packagename.classname.*;

→

It allows to call all static members of the class or

||Om Shree Hanumathe Namaha||

Venu Kumaar.S import static packagename.classname.staticmembername;

→

allows only to call the imported static member.

Ex: import p1.*;

→

We can access all classes from p1 package import p1.A;

→

We can access only class A from p1 package.

import static p1.A.*;

→

We can access all static members of class A from p1 package.

→

Using this import statement we cannot access non-static members, we can't create object, we can't develop subclass from A class. for this purpose we must also write import statement separately for accessing class A as import p1.A;

import static p1.A.a;

→

We can access only the static variable "a".If "a" is a non-static variable it leads to CE:cannot find symbol "static a"

import static p1.A.m1;

→

We can access only static method "m1".

Ex1:Program

package p2;

import static java.lang.System.*;

public class Test {

public static void main(String args[]) { out.println("Hi");

} }

/*Output:

java Test Hi

*/

Ex2:Progam

package p1;

public class Example {

public static int a = 10;

public int x = 20;

public static void m1() {

System.out.println(".p1.Example.m1().");

}

public void m2() {

System.out.println(".p1.Example.m2().");

} }

package p2;

||Om Shree Hanumathe Namaha||

Venu Kumaar.S

import static p1.Example.*;

public class StaticSample {

public static void main(String args[]) { // static int a=10;

// accessing static members

System.out.println("p1.Example.a...."+p1.Example.a);

m1();

// accessing static members with classname // System.out.println(Example.a);//CE:

// Example.m1();//CE:

// accessing non-static members // Example e=new Example();CE:

// System.out.printlm(e.x);

// e.m2();

} }

/*

Output:

java StaticSample p1.Example.a....10 .p1.Example.m1().

*/

package p2;

import p1.Example;

public class NonStaticSample {

public static void main(String args[]) { // accessing static members with classname

System.out.println("...Accessing static members....:");

System.out.println("Example.a...."+Example.a);

Example.m1();

// accessing non-static members

System.out.println("\n...Accessing non-static members....:");

Example e=new Example();

System.out.println("e.x...."+e.x);

e.m2();

} }

/*

Output:

java NonStaticSample ...Accessing static members....:

Example.a....10

||Om Shree Hanumathe Namaha||

Venu Kumaar.S .p1.Example.m1().

...Accessing non-static members....:

e.x....20

.p1.Example.m2().

*/

VarArgs 1.5v

VarArgs 1.5v: Until 1.4v we can't declare a method with variable number of args, if there is any change in number of arguments compulsory we should declare a new method. This approach increases length of the code & reduces readability.

→

To resolve these problem, var-arg method in 1.5v. Hence, from 1.5v onwards we can declare a method with variable number of args such type of methods are called var-arg methods.

→

We can declare var-arg method as : methodname(int... variable);

Ex: m1(int... x);

→

We can invoke this method by passing any number of int values include zero number also.

m1();

m1(10,20);

m1(10);

m1(10,20,30,40);

→

Internally var-arg method is implemented by using single dimensional arrays concept. Hence with in the var-arg method we can differentiate args by using index.

/**@author:Venu Kumar.S @date:Oct 6, 2012

* @fileName:TestVarArgs

.java

*/

public class TestVarArgs {

public static void sum(int... x) {

System.out.println("Summation...:");

int total = 0;

for (int y : x) { total += y;

System.out.println(total);

}

System.out.println("total..=" + total);

}

public static void main(String[] args) { System.out.println("Var Args Demo...");

sum();

sum(10);

sum(20, 30);

sum(40, 50, 60, 70);

} }

||Om Shree Hanumathe Namaha||

Venu Kumaar.S /*

OutPut:

Var Args Demo...

Summation...:

total..=0

Summation...:

10

total..=10

Summation...:

20 50

total..=50

Summation...:

40 90 150 220

total..=220

*/

In document Core_Java By Venu Kumaar (Page 146-155)