How do I search specific value in an array?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.util.Arrays;

public class ArraySearchExample {
    public static void main(String[] args) {
        // We create an array of ints where the search will be done.
        int[] items = {9, 5, 14, 6, 11, 28, 9, 16, 37, 3, 2};

        // The Arrays.binarySearch() require us to sort the array
        // items before we call the method. We can utilize the
        // Arrays.sort() method to do this. If we did not sort the
        // array the result will be undefined, the search process
        // will return a negative result.
        Arrays.sort(items);

        // To search we use Arrays.binarySearch() methods which accept
        // parameters of any array type. To search we passed the array
        // to be searched and the key to be searched for.
        //
        // When the search item exist more than one in the array, this
        // method gives no guarantee which one will be returned.
        int needle = 9;
        int index = Arrays.binarySearch(items, needle);

        // Print out where the 9 number is located in the array.
        System.out.println("Items: " + Arrays.toString(items));
        System.out.println("Item " + needle + " is at index " + index);
    }
}

There result of the code snippet:

Items: [2, 3, 5, 6, 9, 9, 11, 14, 16, 28, 37]
Item 9 is at index 5

How do I sort elements of an array?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.util.Arrays;

public class ArraySortExample {
    public static void main(String[] args) {
        // An array of random numbers
        int[] numbers = {3, 1, 8, 34, 1, 2, 13, 89, 5, 21, 55};
        System.out.println("Before: " + Arrays.toString(numbers));

        // We need to sort these array elements into a correct order
        // from the smallest to the greatest. We will use the Arrays
        // class on java.utils package to do the sort. The sort
        // method of this class are overloaded, so they can take
        // other type of array as well such as byte[], long[],
        // float[], Object[].
        Arrays.sort(numbers);
        System.out.println("After : " + Arrays.toString(numbers));

        // We can also do the sort only for the specified range of
        // array elements.
        float[] money = {1.05f, 99.8f, 3f, 4.55f, 7.23f, 6.50f};
        Arrays.sort(money, 3, money.length);

        // Here we display the sort result, the first and the second
        // element of the array is not included in the sort process.
        System.out.println("Money : " + Arrays.toString(money));
    }
}

And here are the results:

Before: [3, 1, 8, 34, 1, 2, 13, 89, 5, 21, 55]
After : [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
Money : [1.05, 99.8, 3.0, 4.55, 6.5, 7.23]

How do I convert an array of primitives into an array of objects?

By Wayan in Apache Commons, Commons Lang 0 Comment

To convert from primitive arrays into object type arrays, we can use the Apache Commons Lang library. The Commons Lang provides an ArrayUtils class that does this conversion. To convert the other way just use the toPrimitive() method.

package org.kodejava.commons.lang;

import org.apache.commons.lang3.ArrayUtils;

public class ArrayPrimitiveObjectConversionDemo {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        boolean[] booleans = {true, false, false, true};
        float[] decimals = {10.1f, 3.14f, 2.17f};

        Integer[] numbersObjects = ArrayUtils.toObject(numbers);
        Boolean[] booleansObjects = ArrayUtils.toObject(booleans);
        Float[] decimalsObjects = ArrayUtils.toObject(decimals);

        numbers = ArrayUtils.toPrimitive(numbersObjects);
        booleans = ArrayUtils.toPrimitive(booleansObjects);
        decimals = ArrayUtils.toPrimitive(decimalsObjects);
    }
}

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.14.0</version>
</dependency>

Maven Central

How do I check if a file exists?

By Wayan in Core API, IO 0 Comment

To check if a file, or a directory exists we can utilize java.io.File.exists() method. This method return either true or false. Before we can check whether its exists or not we need to create an instance of File that represent an abstract path name of the file or directory. After we have the File instance we can call the exists() method to validate it.

package org.kodejava.io;

import java.io.File;
import java.io.FileNotFoundException;

public class FileExists {
    public static void main(String[] args) throws Exception {
        // Create an abstract definition of configuration file to be
        // read.
        File file = new File("applicationContext-hibernate.xml");

        // Print the exact location of the file in file system.
        System.out.println("File = " + file.getAbsolutePath());

        // If configuration file, applicationContext-hibernate.xml
        // does not exist in the current path throws an exception.
        if (!file.exists()) {
            String message = "Cannot find configuration file!";
            System.out.println(message);
            throw new FileNotFoundException(message);
        }

        // Continue with application logic here!
    }
}

How do I copy some items of an array into another array?

By Wayan in Core API, Lang Package 0 Comment

In the code snippet below we are going to learn how to use the System.arraycopy() method to copy array values. This method will copy array from the specified source array, starting from the element specified by starting position. The array values will be copied to the target array, placed at the specified start position in the target array and will copy values for the specified number of elements.

The code snippet below will copy 3 elements from the letters array and place it in the results array. The copy start from the third elements which is the letter U and will be place at the beginning of the target array.

package org.kodejava.lang;

public class ArrayCopy {
    public static void main(String[] args) {
        // Creates letters array with 5 chars inside it.
        String[] letters = {"A", "I", "U", "E", "O"};

        // Create an array to where we are going to copy
        // some elements of the previous array.
        String[] results = new String[3];

        // Copy 3 characters from letters starting from the
        // third element and put it inside result array
        // beginning at the first element
        System.arraycopy(letters, 2, results, 0, 3);

        // Just print out what were got copied, it will
        // contains U, E, and O
        for (String result : results) {
            System.out.println("result = " + result);
        }
    }
}

The output of the code snippet:

result = U
result = E
result = O