How do I search specific value in an array?

By I Wayan Saryada 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 I Wayan Saryada 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 check if a file exists?

By I Wayan Saryada 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 I Wayan Saryada 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

How do I terminate a Java application?

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

In an application we sometimes want to terminate the execution of our application, for instance because it cannot find the required resource.

To terminate it we can use exit(status) method in java.lang.System class or in the java.lang.Runtime class. When terminating an application we need to provide a status code, a non-zero status assigned for any abnormal termination.

package org.kodejava.lang;

import java.io.File;

public class AppTerminate {
    public static void main(String[] args) {
        File file = new File("config.xml");

        int errCode = 0;
        if (!file.exists()) {
            errCode = 1;
        }

        // When the error code is not zero go terminate
        if (errCode > 0) {
            System.exit(errCode);
        }
    }
}

The call to System.exit(status) is equals to Runtime.getRuntime().exit(status). Actually the System class will delegate the termination process to the Runtime class.

Running the code give the following output because it can’t find the config.xml file.

Process finished with exit code 1