How do I generate a random array of numbers?

By I Wayan Saryada in Core API, Util Package 0 Comment

Using java.util.Random class we can create random data such as boolean, integer, floats, double. First you’ll need to create an instance of the Random class. This class has some next***() methods that can randomly create the data.

package org.kodejava.util;

import java.util.Arrays;
import java.util.Random;

public class RandomDemo {
    public static void main(String[] args) {
        Random r = new Random();

        // generate some random boolean values
        boolean[] booleans = new boolean[10];
        for (int i = 0; i < booleans.length; i++) {
            booleans[i] = r.nextBoolean();
        }
        System.out.println(Arrays.toString(booleans));

        // generate a uniformly distributed int random numbers
        int[] integers = new int[10];
        for (int i = 0; i < integers.length; i++) {
            integers[i] = r.nextInt();
        }
        System.out.println(Arrays.toString(integers));

        // generate a uniformly distributed float random numbers
        float[] floats = new float[10];
        for (int i = 0; i < floats.length; i++) {
            floats[i] = r.nextFloat();
        }
        System.out.println(Arrays.toString(floats));

        // generate a Gaussian normally distributed random numbers
        double[] doubles = new double[10];
        for (int i = 0; i < doubles.length; i++) {
            doubles[i] = r.nextGaussian();
        }
        System.out.println(Arrays.toString(doubles));
    }
}

The result of the code snippet above are:

[true, true, false, true, false, true, true, false, false, true]
[34195704, 1462972230, -475641915, -1531017612, 332184915, 1555901473, -276309016, 1433394157, -451221924, -1178823255]
[0.3040716, 0.28814012, 0.34028566, 0.021003246, 0.49158317, 0.37954164, 0.5403056, 0.54187375, 0.7157934, 0.5964742]
[1.051268591002577, -1.1283332046139989, 0.8351395528722437, -0.24598168031182968, 0.7123515366756693, -0.9661681996105319, -1.6107009669125059, 0.43994917963255387, 1.1309345726165914, 1.2321618489324313]

For an example to create random number using the Math.random() method see How do I create random number?.

How do I reverse a string by word?

By I Wayan Saryada in Core API, Util Package 0 Comment

In the other examples on this website you might have seen how to reverse a string using StringBuffer, StringUtils from Apache Commons Lang library or using the CharacterIterator.

In this example you’ll see another way that you can use to reverse a string by word. Here we use the StringTokenizer and the Stack class.

package org.kodejava.util;

import java.util.Stack;
import java.util.StringTokenizer;

public class ReverseStringByWord {
    public static void main(String[] args) {
        // The string that we'll reverse
        String text = "Jackdaws love my big sphinx of quartz";

        // We use StringTokenize to get each word of the string. You might try
        // to use the String.split() method if you want.
        StringTokenizer st = new StringTokenizer(text, " ");

        // To reverse it we can use the Stack class, which implements the LIFO
        // (last-in-first-out).
        Stack<String> stack = new Stack<>();
        while (st.hasMoreTokens()) {
            stack.push(st.nextToken());
        }

        // Print each word in reverse order
        while (!stack.isEmpty()) {
            System.out.print(stack.pop() + " ");
        }
    }
}

How do I convert varargs to an array?

By I Wayan Saryada in Core API, Lang Package 0 Comment

Varargs can be seen as a simplification of array when we need to pass a multiple value as a method parameter. Varargs itself is an array that automatically created, for these reason you will be enabled to do things you can do with array to varargs.

In the example below you can see the messages parameter can be assigned to the String array variables, we can call the length method to the messages parameter as we do with the array. So actually you don’t need to convert varargs to array because varargs is array.

package org.kodejava.lang;

public class VarargsToArray {
    public static void main(String[] args) {
        printMessage("Hello ", "there", ", ", "how ", "are ", "you", "?");
    }

    public static void printMessage(String... messages) {
        String[] copiedMessage = messages;
        for (int i = 0; i < messages.length; i++) {
            System.out.print(copiedMessage[i]);
        }
    }
}

How do I remove trailing white space from a string?

By I Wayan Saryada in Core API, Lang Package 0 Comment

The trim() method of a String class removes both leading and trailing white space from a string. In this example we use a regular expression to remove only the trailing white spaces from a string.

package org.kodejava.lang;

public class TrailingSpace {
    public static void main(String[] args) {
        String text = "     tattarrattat     ";
        System.out.println("Original      = " + text);
        System.out.println("text.length() = " + text.length());

        // Using a regular expression to remove only the trailing white space in
        // a string
        text = text.replaceAll("\\s+$", "");
        System.out.println("Result        = " + text);
        System.out.println("text.length() = " + text.length());
    }
}

Original      =      tattarrattat     
text.length() = 22
Result        =      tattarrattat
text.length() = 17

How do I remove leading white space from a string?

By I Wayan Saryada in Core API, Lang Package 0 Comment

The trim() method of a String class removes both leading and trailing white space from a string. In this example we use a regular expression to remove only the leading white spaces from a string.

package org.kodejava.lang;

public class LeadingSpace {
    public static void main(String[] args) {
        String text = "     tattarrattat     ";
        System.out.println("Original      = " + text);
        System.out.println("text.length() = " + text.length());

        // Using regular expression to remove only the leading white
        // space in string
        text = text.replaceAll("^\\s+", "");
        System.out.println("Result        = " + text);
        System.out.println("text.length() = " + text.length());
    }
}

Original      =      tattarrattat     
text.length() = 22
Result        = tattarrattat     
text.length() = 17