How do I align string print out in left, right, center alignment?

The following code snippet will teach you how to align string in left, right or center alignment when you want to print out string to a console. We will print the string using the printf(String format, Object... args) method. The format specifier / parameter defines how the string will be formatted for output and the args is the value that will be formatted.

The format parameter / specifier include flags, width, precision and conversion-characters in the order shown below. The square brackets in the notation means the part is an optional parameter.

% [flags] [width] [.precision] conversion-character
Flags Description
- left-align the output, when not specified the default is to right-align
+ print (+) or (-) sign for numeric value
0 zero padded a numeric value
, comma grouping separator for number greater that 1000
space will output a (-) symbol for negative value and a space if positive
Conversion Description
s string, use capital S to uppercase the strings
c character, use capital C to uppercase the characters
d integer: byte, short, integer, long
f floating point number: float, double
n new line

Width: Defines the field width for printing out the value of argument. It also represents the minimum number of characters to
be printed out to the output.

Precision: For floating-point conversion the precision define the number of digits of precision in a floating point value. For string value this will extract the substring.

To center the string for output we use the StringUtils.center() method from the Apache Commons Lang library. This method will center-align the string str in a larger string of size using the default space character (‘ ‘). You can supply the third parameter to define your own space character / string.

package org.kodejava.example.lang;

import org.apache.commons.lang3.StringUtils;

import java.time.LocalDate;
import java.time.Month;
import java.time.temporal.ChronoUnit;

public class StringAlignment {
    private static Object[][] people = {
        {"Alice", LocalDate.of(2000, Month.JANUARY, 1)},
        {"Bob", LocalDate.of(1989, Month.DECEMBER, 15)},
        {"Carol", LocalDate.of(1992, Month.JULY, 24)},
        {"Ted", LocalDate.of(2006, Month.MARCH, 13)},
    };

    public static void main(String[] args) {
        String nameFormat = "| %1$-20s | ";
        String dateFormat = " %2$tb %2$td, %2$tY  | ";
        String ageFormat = " %3$3s |%n";
        String format = nameFormat.concat(dateFormat).concat(ageFormat);
        String line = new String(new char[48]).replace('\0', '-');

        System.out.println(line);
        System.out.printf("|%s|%s|%s|%n",
            StringUtils.center("Name", 22),
            StringUtils.center("Birth Date", 16),
            StringUtils.center("Age", 6));
        System.out.println(line);

        for (Object[] data : people) {
            System.out.printf(format,
                data[0], data[1],
                ChronoUnit.YEARS.between((LocalDate) data[1], LocalDate.now()));
        }

        System.out.println(line);
    }
}

Here is the output of our code snippet above:

------------------------------------------------
|         Name         |   Birth Date   | Age  |
------------------------------------------------
| Alice                |  Jan 01, 2000  |   17 |
| Bob                  |  Dec 15, 1989  |   27 |
| Carol                |  Jul 24, 1992  |   24 |
| Ted                  |  Mar 13, 2006  |   10 |
------------------------------------------------

Maven Dependencies

<!-- http://repo1.maven.org/maven2/org/apache/commons/commons-lang3/3.6/commons-lang3-3.6.jar -->
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.6</version>
</dependency>

How do I generate random string?

package org.kodejava.example.security;

import java.security.SecureRandom;
import java.util.Random;

public class RandomString {
    public static final String SOURCES =
            "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";

    public static void main(String[] args) {
        RandomString rs = new RandomString();
        System.out.println(rs.generateString(new Random(), SOURCES, 10));
        System.out.println(rs.generateString(new Random(), SOURCES, 10));
        System.out.println(rs.generateString(new SecureRandom(), SOURCES, 15));
        System.out.println(rs.generateString(new SecureRandom(), SOURCES, 15));
    }

    /**
     * Generate a random string.
     *
     * @param random the random number generator.
     * @param characters the characters for generating string.
     * @param length the length of the generated string.
     * @return
     */
    public String generateString(Random random, String characters, int length) {
        char[] text = new char[length];
        for (int i = 0; i < length; i++) {
            text[i] = characters.charAt(random.nextInt(characters.length()));
        }
        return new String(text);
    }
}

Example string produced by the code snippets are:

uxEUFqTqS0
vr89vdF4gh
ysYF9XEHhO5FtDf
aBANhrLObZ1XLJi

How to split a string by a number of characters?

The following code snippet will show you how to split a string by numbers of characters. We create a method called splitToNChars() that takes two arguments. The first arguments is the string to be split and the second arguments is the split size.

This splitToNChars() method will split the string in a for loop. First we’ll create a List object that will store parts of the split string. Next we do a loop and get the substring for the defined size from the text and store it into the List. After the entire string is read we convert the List object into an array of String by using the List‘s toArray() method.

Let’s see the code snippet below:

package org.kodejava.example.lang;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class SplitStringForEveryNChar {
    public static void main(String[] args) {
        String text = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        System.out.println(Arrays.toString(splitToNChar(text, 3)));
        System.out.println(Arrays.toString(splitToNChar(text, 4)));
        System.out.println(Arrays.toString(splitToNChar(text, 5)));
    }

    /**
     * Split text into n number of characters.
     *
     * @param text the text to be split.
     * @param size the split size.
     * @return an array of the split text.
     */
    private static String[] splitToNChar(String text, int size) {
        List<String> parts = new ArrayList<>();

        int length = text.length();
        for (int i = 0; i < length; i += size) {
            parts.add(text.substring(i, Math.min(length, i + size)));
        }
        return parts.toArray(new String[0]);
    }
}

When run the code snippet will output:

[ABC, DEF, GHI, JKL, MNO, PQR, STU, VWX, YZ]
[ABCD, EFGH, IJKL, MNOP, QRST, UVWX, YZ]
[ABCDE, FGHIJ, KLMNO, PQRST, UVWXY, Z]

How do I split a string with multiple spaces?

This code snippet show you how to split string with multiple white-space characters. To split the string this way we use the "\s+" regular expression. The white-space characters include space, tab, line-feed, carriage-return, new line, form-feed.

Let’s see the code snippet below:

package org.kodejava.example.lang;

import java.util.Arrays;

public class SplitStringMultiSpaces {
    public static void main(String[] args) {
        String text = "18/08/2012    SHOES      RUNNING RED   99.9 USD";

        // Split the string using the \s+ regex to split multi spaces
        // line of text.
        String[] items = text.split("\\s+");
        System.out.println("Length = " + items.length);
        System.out.println("Items  = " + Arrays.toString(items));
    }
}

The result of the code snippet is:

Length = 6
Items  = [18/08/2017, SHOES, RUNNING, RED, 99.9, USD]

How do I use string in switch statement?

Starting from Java 7 release you can now use a String in the switch statement. On the previous version we can only use constants type of byte, char, short, int (and their corresponding reference / wrapper type) or enum constants in the switch statement.

The code below give you a simple example on how the Java 7 extended to allow the use of String in switch statement.

package org.kodejava.example.basic;

public class StringInSwitchExample {
    public static void main(String[] args) {
        String day = "Sunday";
        switch (day) {
            case "Sunday":
                System.out.println("doSomething");
                break;
            case "Monday":
                System.out.println("doSomethingElse");
                break;
            case "Tuesday":
            case "Wednesday":
                System.out.println("doSomeOtherThings");
                break;
            default:
                System.out.println("doDefault");
                break;
        }
    }
}

How do I breaks a text or sentence into words?

At first it might look simple. We can just split the text using the String.split(), the word is split using space. But what if a word ends with questions marks (?) or exclamation marks (!) instead? There might be some other rules that we also need to care.

Using the java.text.BreakIterator makes it much simpler. The class’s getWordInstance() factory method creates a BreakIterator instance for words break. Instantiating a BreakIterator and passing a locale information makes the iterator to breaks the text or sentence according the rule of the locale. This is really helpful when we are working with a complex language such as Japanese or Chinese.

Let us see an example of using the BreakIterator below.

package org.kodejava.example.text;

import java.text.BreakIterator;
import java.util.Locale;

public class BreakIteratorExample {
    public static void main(String[] args) {
        String data = "The quick brown fox jumps over the lazy dog.";
        String search = "dog";

        // Gets an instance of BreakIterator for word break for the
        // given locale. We can instantiate a BreakIterator without
        // specifying the locale. The locale is important when we
        // are working with languages like Japanese or Chinese where
        // the breaks standard may be different compared to English.
        BreakIterator bi = BreakIterator.getWordInstance(Locale.US);

        // Set the text string to be scanned.
        bi.setText(data);

        // Iterates the boundary / breaks
        System.out.println("Iterates each word: ");
        int count = 0;
        int lastIndex = bi.first();
        while (lastIndex != BreakIterator.DONE) {
            int firstIndex = lastIndex;
            lastIndex = bi.next();

            if (lastIndex != BreakIterator.DONE
                && Character.isLetterOrDigit(data.charAt(firstIndex))) {
                String word = data.substring(firstIndex, lastIndex);
                System.out.printf("'%s' found at (%s, %s)%n", word, firstIndex, lastIndex);

                // Counts how many times the word dog occurs.
                if (word.equalsIgnoreCase(search)) {
                    count++;
                }
            }
        }

        System.out.println("Number of word '" + search + "' found = " + count);
    }
}

Here are the program output:

Iterates each word: 
'The' found at (0, 3)
'quick' found at (4, 9)
'brown' found at (10, 15)
'fox' found at (16, 19)
'jumps' found at (20, 25)
'over' found at (26, 30)
'the' found at (31, 34)
'lazy' found at (35, 39)
'dog' found at (40, 43)
Number of word 'dog' found = 1

How do I get char value of a string at a specified position?

The chartAt() method of the String class returns the char value at the specified index. An index ranges from 0 to length() - 1. If we specified an index beyond of this range a StringIndexOutOfBoundsException exception will be thrown.

These method use zero based index which means the first char value of the sequence is at index 0, the next at index 1, and so on, as for array indexing.

package org.kodejava.example.lang;

public class CharAtExample {
    public static void main(String[] args) {
        String[] colors = {"black", "white", "brown", "green", "yellow", "blue"};

        for (String color : colors) {
            // Get char value of a string at index number 3. Because
            // the index is zero based we'll get the fourth character
            // of each color in the array.
            char value = color.charAt(3);
            System.out.printf("The fourth char of %s is '%s'.%n", color, value);
        }

    }
}

Here is the program output:

The fourth char of black is 'c'
The fourth char of white is 't'
The fourth char of brown is 'w'
The fourth char of green is 'e'
The fourth char of yellow is 'l'
The fourth char of blue is 'e'

How do I sort string of numbers in ascending order?

In the following example we are going to sort a string containing the following numbers "2, 5, 9, 1, 10, 7, 4, 8" in ascending order so we will get the result of "1, 2, 4, 5, 7, 8, 9, 10".

package org.kodejava.example.util;

import java.util.Arrays;
import java.util.Collections;

public class SortStringNumber {
    public static void main(String[] args) {
        // We have some string numbers separated by comma. First we
        // need to split it so we can get each individual number.
        String data = "2, 5, 9, 1, 10, 7, 4, 8";
        String[] numbers = data.split(",");

        // Convert the string numbers into Integer and placed it into
        // an array of Integer.
        Integer[] intValues = new Integer[numbers.length];
        for (int i = 0; i < numbers.length; i++) {
            intValues[i] = Integer.parseInt(numbers[i].trim());
        }

        // Sort the number in ascending order using the
        // Collections.sort() method.
        Collections.sort(Arrays.asList(intValues));

        // Convert back the sorted number into string using the
        // StringBuilder object. Prints the sorted string numbers.
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < intValues.length; i++) {
            Integer intValue = intValues[i];
            builder.append(intValue);
            if (i < intValues.length - 1) {
                builder.append(", ");
            }
        }
        System.out.println("Before = " + data);
        System.out.println("After  = " + builder.toString());
    }
}

When we run the program we will get the following output:

Before = 2, 5, 9, 1, 10, 7, 4, 8
After  = 1, 2, 4, 5, 7, 8, 9, 10

How do I determine whether a string is a palindrome?

This code checks a string to determine if it is a palindrome or not. A palindrome is a word, phrase, or sequence that reads the same backward as forward.

package org.kodejava.example.lang;

public class PalindromeChecker {

    public static void main(String[] args) {
        String text = "Sator Arepo Tenet Opera Rotas";

        PalindromeChecker checker = new PalindromeChecker();
        System.out.println("Is palindrome = " + checker.isPalindrome(text));
    }

    /**
     * This method checks the string for palindrome. We use StringBuilder to
     * reverse the original string.
     *
     * @param text
     * @return
     */
    private boolean isPalindrome(String text) {
        System.out.println("Original text = " + text);

        String reverse = new StringBuilder(text).reverse().toString();
        System.out.println("Reverse text  = " + reverse);

        // Compare the original text with the reverse one and ignoring its case
        return text.equalsIgnoreCase(reverse);
    }
}

How do I convert InputStream to String?

This example will show you how to convert an InputStream into String. In the code snippet below we read a data.txt file, could be from common directory or from inside a jar file.

package org.kodejava.example.io;

import java.io.*;

public class StreamToString {

    public static void main(String[] args) throws Exception {
        StreamToString demo = new StreamToString();

        // Get input stream of our data file. This file can be in
        // the root of you application folder or inside a jar file
        // if the program is packed as a jar.
        InputStream is = demo.getClass().getResourceAsStream("/data.txt");

        // Call the method to convert the stream to string
        System.out.println(demo.convertStreamToString(is));
    }

    private String convertStreamToString(InputStream stream) throws IOException {
        // To convert the InputStream to String we use the
        // Reader.read(char[] buffer) method. We iterate until the
        // Reader return -1 which means there's no more data to
        // read. We use the StringWriter class to produce the string.
        if (stream != null) {
            Writer writer = new StringWriter();

            char[] buffer = new char[1024];
            try {
                Reader reader = new BufferedReader(new InputStreamReader(stream, "UTF-8"));
                int n;
                while ((n = reader.read(buffer)) != -1) {
                    writer.write(buffer, 0, n);
                }
            } finally {
                stream.close();
            }
            return writer.toString();
        }
        return "";
    }
}