Getting environment values

There are two ways for getting the environment values in Java:

1. We can use System.getProperty(systemPropertyString) to retrieve the values, such as java.version, java.home, os.name, user.name, user.home, user.dir, java.io.tmpdir etc;

2. Use System.getenv to enumerate all the system environment:

==============================================================
import java.util.*;

public class ListEnv {

public static void listAllEnv(){

Map variables = System.getenv();
Set variableNames = variables.keySet();

Iterator nameIterator = variableNames.iterator();

for(int index=0; index < variableNames.size(); index++){

String name = (String) nameIterator.next();
String value = (String) variables.get(name);
System.out.println(name + "=" + value);

}

}

public static void main(String[] args) {

listAllEnv();

}

}
==============================================================

Q11: number composition

Q: How many three digit numbers can you generate with 1, 2, 3, 4. The numbers are not duplicated and each number doesn't have duplicate digits.

A:

===========================================
import java.util.Vector;

public class NumberComposition {

private static Vector nums = new Vector();

public static void generateNumbers(){

int num;

for(int i=1; i <= 4; i++){

num =0;
for(int j=1; j <= 4; j++){

for(int k=1; k <= 4; k++){

if((i!=j) && (i!=k) && (j!=k)){

num = i* 100 + j*10 + k;
nums.add(num);

}else continue;

}

}

}

}

public static int getNumberCounter(){

return nums.size();

}

public static void printNumbers(){

for(int i=0; i < nums.size(); i++){

System.out.print(nums.get(i) + " ");

}

}

public static void main(String[] args) {

generateNumbers();
System.out.println("Total number: " + getNumberCounter());
printNumbers();

}

}
==========================================

result:
Total number: 24
123 124 132 134 142 143 213 214 231 234 241 243 312 314 321 324 341 342 412 413 421 423 431 432

Java mail SMTP sample code

This sample code demonstrates the minimum Java code for using regular SMTP service and GMail SMTP service.

First of all, we download the Java Activation Framework and JavaMail packages.

Sample code is followed:

===============================================================

import java.security.Security;
import java.util.Date;
import java.util.Properties;

import javax.mail.Authenticator;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.NoSuchProviderException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.AddressException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class AlarmMail {

public void sendGMail() {

Security.addProvider(new com.sun.net.ssl.internal.ssl.Provider());
final String SSL_FACTORY = "javax.net.ssl.SSLSocketFactory";

// Get a Properties object, and set the parameters of mail service
Properties props = new Properties();
props.setProperty("mail.smtp.host", "smtp.gmail.com");
props.setProperty("mail.smtp.socketFactory.class", SSL_FACTORY);
props.setProperty("mail.smtp.socketFactory.fallback", "false");
props.setProperty("mail.smtp.port", "465");
props.setProperty("mail.smtp.socketFactory.port", "465");
props.put("mail.smtp.auth", "true");
final String username = "shuzhanqiang@gmail.com";
final String password = "******";
Session session = Session.getDefaultInstance(props,

new Authenticator() {

protected PasswordAuthentication getPasswordAuthentication() {

return new PasswordAuthentication(username, password);

}

});

session.setDebug(true);

// -- Create a new message --
Message msg = new MimeMessage(session);

// -- Set the FROM, TO, and Mail contain fields --
try {

msg.setFrom(new InternetAddress(username));
msg.setRecipients(Message.RecipientType.TO, InternetAddress.parse(
"shu_zhq@yahoo.com", false));
msg.setSubject("Hello");
msg.setText("Hello");
msg.setSentDate(new Date());
System.out.println("Start sending");
Transport.send(msg);

} catch (AddressException e) {

e.printStackTrace();

} catch (MessagingException e) {

e.printStackTrace();

}

System.out.println("Message sent.");

}

private String mailhost = "mail.abc.com";
private String user = "qiang@abc.com";
private String password = "123456";
private String from, to, cc, bcc;
private String subject;
private String text;
private String mailer = "smtpsend";
private boolean ssl = false;
private boolean verbose;

public void sendMsg() {

try {

InternetAddress[] address = null;

// Get a Properties object, and set the parameters of mail service
Properties props = new Properties();
props.put("mail.smtp.host", mailhost);
props.setProperty("mail.smtp.port", "25");
props.put("mail.smtp.auth", "true");
javax.mail.Session sessmail = javax.mail.Session.getInstance(props);
sessmail.setDebug(true);
MimeMessage msg = new MimeMessage(sessmail);
msg.setFrom(new InternetAddress(user));

address = InternetAddress.parse(to, false);
msg.setRecipients(Message.RecipientType.TO, address);

msg.setSubject(subject);
msg.setSentDate(new Date());
msg.setText(text, "UTF-8");
Transport transport = sessmail.getTransport("smtp");
transport.connect(mailhost, user, password);
transport.sendMessage(msg, msg.getAllRecipients());
transport.close();

} catch (AddressException e) {

e.printStackTrace();

} catch (NoSuchProviderException e) {

e.printStackTrace();

} catch (MessagingException e) {

e.printStackTrace();

}

}


public static void main(String[] args) {

AlarmMail am = new AlarmMail();
am.setFrom("shu_zhq@gmail.com");
am.setTo("shu_zhq@yahoo.com");
am.setSubject("Help");
am.setText("Help.");
am.sendMsg();

am.sendGMail();

}

public String getBcc() {

return bcc;

}

public void setBcc(String bcc) {

this.bcc = bcc;

}

public String getCc() {

return cc;

}

public void setCc(String cc) {

this.cc = cc;

}

public String getFrom() {

return from;

}

public void setFrom(String from) {

this.from = from;

}

public String getMailer() {

return mailer;

}

public void setMailer(String mailer) {

this.mailer = mailer;

}

public String getMailhost() {

return mailhost;

}

public void setMailhost(String mailhost) {

this.mailhost = mailhost;

}

public String getPassword() {

return password;

}

public void setPassword(String password) {

this.password = password;

}

public boolean isSsl() {

return ssl;

}

public void setSsl(boolean ssl) {

this.ssl = ssl;

}

public String getSubject() {

return subject;

}

public void setSubject(String subject) {

this.subject = subject;

}

public String getText() {

return text;

}

public void setText(String text) {

this.text = text;

}

public String getTo() {

return to;

}

public void setTo(String to) {

this.to = to;

}

public String getUser() {

return user;

}

public void setUser(String user) {

this.user = user;

}

public boolean isVerbose() {

return verbose;

}

public void setVerbose(boolean verbose) {

this.verbose = verbose;

}

}

DNS Configuration in Fedora 4

This is only to set up a DNS environment for an application testing, so it only setup a simple domain look up function, and doesn't use so much functions, such as bind-chroot

DNS setup steps:

1. Design the mapping between domain name and IP address. Here, I use zhanqiang.net and 192.168.1.110;

2. Check if BIND(Berkeley Internet Name Domain) has been installed: rpm -qa | grep bind

3. Add some lines in /etc/named.conf

change
=======================================
zone "0.in-addr.arpa" IN {

type master;
file "named.zero";
allow-update { none; };

};
include "/etc/rndc.key";

=======================================
to
=======================================
zone "0.in-addr.arpa" IN {

type master;
file "named.zero";
allow-update { none; };

};

zone "zhanqiang.net" IN {

type master;
file "zhanqiang.net.zone";
allow-update { none; };

};

include "/etc/rndc.key";
=======================================

4. create and edit /var/named/zhanqiang.net.zone
=======================================
$TTL 86400
@　　　IN　　SOA 　　dns.zhanqiang.net.　　root.zhanqiang.net. (

1997022700 ; Serial
28800 ; Refresh
7000 ; Retry
1800000 ; Expire
86400 ) ; Minimum

@　　IN　　NS　　　 dns.zhanqiang.net.
@　　IN　MX　10　　　dns.zhanqiang.net.
dns　　　　IN　A 192.168.1.110
www　　　　IN　CNAME 　　　　dns
=======================================

5. restart named(DNS) service: service named restart

6. check firewall if the port 53 has been blocked;

7. run neat or edit /etc/resolve.conf for changing the network card DNS setting in order to use the DNS service in 192.168.1.110

8. test the DNS with ping, host, and nslookup commands

Now it is done.

Q10: Bouncing Ball

Q: a ball is dropped from 100 meters and bounce back to half of previous height. How many meters does it pass when it hits the ground at 10th time, and the height of it 10th bounce back?

A:


public class BallBounce {

/**
* Because the height is half of the previous one each bounce back,
* the height is divided by 2 each time.
* @param initHeight the initial height
* @param times the number of bounce back
* @return the height of bounce
*/
public static float getHeight(float initHeight, int times){

for(int i=0; i< times; i++){

initHeight /= 2;

}
return initHeight;

}

/**
* When ball hits ground n times, it bounces back n-1 time.
* Therefore, it passes initHeight plus the multiplication of 2 and height of each bounce.
* @param initHeight the initial height
* @param times the number that ball hits the ground
* @return the meters of the ball passed
*/
public static float getBallPass(float initHeight, int hitTimes){

float p = initHeight;
for(int i=0; i<(hitTimes-1); i++){

p += getHeight(initHeight, i+1)*2;

}
return p;

}

public static void main(String[] args) {

int times = 5;
System.out.println("When the ball hits 10th ground, it passes " + getBallPass(100, times) + " meters, and it bounces back " + getHeight(100, times));

}

}

result:
When the ball hits 10th ground, it passes 299.60938 meters, and it bounces back 0.09765625.

Q9: Perfect Number

Q: find out all perfect numbers that are less than 1,000.

a perfect number is defined as an integer which is the sum of its proper positive divisors, that is, the sum of the positive divisors not including the number. For example, the first perfect number is 6, because 1, 2 and 3 are its proper positive divisors and 1 + 2 + 3 = 6. Definition is from wikipedia.org

A:
import java.util.Vector;

public class PerfectNumber {

private static Vector v ;

private static void getAllFactors(int n){

v = new Vector();
if(n <= 2) return;
v.add(1);
int sqrt = (int)Math.pow(n, 0.5)+1;
for(int i=2; i < sqrt; i++){

if((n%i) == 0){

v.add(i);
v.add(n/i);

}

}

}

private static boolean isPerfectNumber(int num){

getAllFactors(num);
int sum = 0;
for(int i=0; i < v.size(); i++){

sum += v.get(i);

}
// System.out.println(num + " sum: " + sum);
if(sum == num) return true;
return false;

}

public static void printPerfectNumber(int range){

for(int i=1; i < range; i++){

if(isPerfectNumber(i)){

System.out.print(i + ", ");

}

}

}
public static void main(String[] args) {

System.out.println("Perfect numbers between 0 and 1000: ");
PerfectNumber.printPerfectNumber(1000);

}

}

Result:
Perfect numbers between 0 and 1000:
6, 28, 496,

Q8: sum calculation

Q: calculate the sum of s in s = a + aa + a...a. a is a number. The last number is a a digits number. For example, a is 5, then the formula is s = 5 + 55 + 555 + 5555 + 55555.

A:

public class Sum {

private static int getNumber(int a, int len){

int num =0;
for(int i=1; i<=len; i++){

num = num * 10 + a;

}
System.out.println("num " + len +": " + num);
return num;

}

public static int getSum(int a){

int sum =0;
for(int i=1; i<=a; i++){

sum += getNumber(a, i);

}
return sum;

}
public static void main(String[] args) {

System.out.println("Sum for 5: " + Sum.getSum(5));

}

}

result:
num 1: 5
num 2: 55
num 3: 555
num 4: 5555
num 5: 55555
Sum for 5: 61725

Q7: Input statistics

Q: Counting the quantity of letters, numbers, space, and others in a input line.

A:

import java.util.Scanner;

public class InputCounting {

public static int countLetters(String is){

byte b[] = is.getBytes();
int cnt = 0;
for(int i=0; i < b.length; i++){

if(Character.isLetter(b[i])) cnt++;

}
return cnt;

}

public static int countNumbers(String is){

byte b[] = is.getBytes();
int cnt = 0;
for(int i=0; i < b.length; i++){

if(Character.isDigit(b[i])) cnt++;

}
return cnt;

}

public static int countSpaces(String is){

byte b[] = is.getBytes();
int cnt = 0;
for(int i=0; i < b.length; i++){

if(Character.isSpaceChar(b[i])) cnt++;

}
return cnt;

}

public static int countOthers(String is){

byte b[] = is.getBytes();
int cnt = 0;
for(int i=0; i < b.length; i++){

if(!(Character.isSpaceChar(b[i]) ||

Character.isDigit(b[i]) ||
Character.isLetter(b[i])))
cnt++;

}

}
return cnt;

}

public static void main(String[] args) {

Scanner s = new Scanner(System.in);
String input;
while(true){

System.out.print("Please input the counted String: ");
input = s.nextLine();
if(input.equalsIgnoreCase("Quit")) break;
System.out.println("Letter quantity: " + InputCounting.countLetters(input));
System.out.println("Number quantity: " + InputCounting.countNumbers(input));
System.out.println("Space quantity: " + InputCounting.countSpaces(input));
System.out.println("Others quantity: " + InputCounting.countOthers(input));

}

}

}

result:
Please input the counted String: What are the counters for "123456"?
Letter quantity: 21
Number quantity: 6
Space quantity: 5
Others quantity: 3
Please input the counted String: Quit

Q6: Lowest common denominator and Greatest common divisor

Q: find the Lowest Common Denominator(LCD) and the Greatest Common Divisor(GCD) for two given integers.

The lowest common denominator or least common denominator (abbreviated LCD) is the least common multiple of the denominators of a set of vulgar fractions.

The greatest common divisor (gcd), sometimes known as the greatest common factor (gcf) or highest common factor (hcf), of two non-zero integers, is the largest positive integer that divides both numbers without remainder.

The definitions are from Wikipedia.org

A:

public class GcdAndLcm {

// This is using Euclidean algorithm.
public static int getGreatestCommonDivisor(int a, int b){

// make sure that a is greater than b
if(b > a){

int c = a; a = b; b = c;

}

if((a % b) == 0) return b;
else if( (a % b) == 1) return 1;
else return getGreatestCommonDivisor(b, (a%b));

}

public static int getLeastCommonMultiple(int a, int b){

return (a * b / getGreatestCommonDivisor(a, b));

}

public static void main(String[] args) {

System.out.println("Greatest Common Divisor for 84 and 18 is " + GcdAndLcm.getGreatestCommonDivisor(84, 18));
System.out.println("Least Common Multiple for 84 and 18 is " + GcdAndLcm.getLeastCommonMultiple(84, 18));

}

}

result:
Greatest Common Divisor for 84 and 18 is 6
Least Common Multiple for 84 and 18 is 252

Q5: Mark Rank

Q: Ranking a mark:

1. Greater than or equal to 90, it is A;
2. Between 60 and 89, it is B;
3. Less than 60, it is C.

A:

public class MarkRank {

public static char rankMark(int mark){

if(mark >= 90) return 'A';
else if((mark <=89) && (mark >=60)) return 'B';
else return 'C';

}

public static void main(String[] args) {

System.out.println("Mark 95: " + MarkRank.rankMark(95));
System.out.println("Mark 78: " + MarkRank.rankMark(78));
System.out.println("Mark 59: " + MarkRank.rankMark(59));

}

}

Q4: Integer factorization.

Q: factorize a given integer. For example: 90 = 2*3*3*5;

A:
Assuming a number n to be factorized. following steps:
1. from 1 to n, find the smallest prime number a by which n is divided;
2. if a equal to n, then exit;
3. if n is divided by a, then performs the division continuously, and the result is assigned to n;
4. if n is not divided by a, try the next number a = a + 1, and repeat 2 to 4;


public class IntegerFactoring {

private static int getFactor(int num, int startpoint){

if(num <= 1) return 1;
for(int i=startpoint+1; i<=num; i++){

if((num % i) == 0) return i;

}
return 1;

}

public static void printFactoring(int n){

int f = 1;
f=getFactor(n, f);
System.out.print(n + "=" + f);
n = n/f;
f--;
while((f=getFactor(n, f)) !=1){

while(n%f ==0){

n = n/f;
System.out.print("*" + f);

}

}

}

public static void main(String[] args) {

IntegerFactoring.printFactoring(90);

}

}

result:
90=2*3*3*5

Q3: Armstrong Number(Narcissistic number)

Q: Print out all Narcissistic numbers between 100 and 999.

In number theory, a narcissistic number or pluperfect digital invariant (PPDI) or Armstrong number is a number that in a given base is the sum of its own digits to the power of the number of digits.

For example, the decimal (Base 10) number 153 is an Armstrong number, because:

1³ + 5³ + 3³ = 153

A:
public class Armstrong {

private static boolean isArmstrong(int n){

int base = n;
int size = Integer.toString(n).length();
int sum = 0, d=0;

for(int i=0; i < size; i++){

d = base %10;
base /=10;
sum += Math.pow(d, size);

}
if(sum == n) return true;
else return false;

}

public static int getArmstrongQuantity(int root, int floor){

int cnt =0;
for(int i=root; i < floor; i++){

if(isArmstrong(i)){

System.out.print(i + ", ");
cnt++;

}

}
System.out.println();
return cnt;

}

public static void main(String[] args) {

System.out.println("There are " +

Armstrong.getArmstrongQuantity(100, 999) +
" armstrong numbers between 100 and 999.");

}

}

result:
153, 370, 371, 407,
There are 4 armstrong numbers between 100 and 999.

Q2: Prime numbers between 100 and 200

Q: How many prime numbers are there between 100 and 200?

A:

public class PrimeNumber {

private static boolean isPrimeNumber(int num){

int e = (int)Math.pow(num, 0.5) + 1;
for(int i = 2; i< e; i++){

/* detect if the number is divided by a integer */
if( (num%i) == 0)

return false;

}
return true;

}

}

public static int getPrimeNumberQuantity(int root, int floor){

if(floor < 2) return 0;

int q = 0;
for(int i=root; i < floor; i++){

if(isPrimeNumber(i)){

q++;
System.out.print(i + ", ");

}

}
System.out.println();
return q;

}

public static void main(String[] args) {

int m = PrimeNumber.getPrimeNumberQuantity(100, 200);
System.out.println("There are " + m + " prime numbers between 100 and 200.");

}

}


Result:

101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199,
There are 21 prime numbers between 100 and 200.