How do I use the diamond syntax?

By I Wayan Saryada in Basic, Core API 0 Comment

In Java 7 a new feature called diamond syntax or diamond operator was introduced. This diamond syntax <> simplify how we instantiate generic type variables. In the previous version of Java when declaring and instantiating generic types we’ll do it like the snippet below:

List<String> names = new ArrayList<String>();
Map<String, List<Integer>> map = new HashMap<String, List<Integer>>();

As you can see in the snippet, we were repeating our self by defining the generic type two times. We define the object type we’ll be stored in the List and the Map on both left and the right side. By using the diamond syntax the compiler will infer the type of the right side expression argument automatically. So in Java 7 we can write the above code snippet like this:

List<String> names = new ArrayList<>();
Map<String, List<Integer>> map = new HashMap<>();

This make our code simpler and more readable, and by using the diamond syntax the compiler will ensure that we have the generic type-safe checking available in our code. This will make any error due to type incompatibility captured at compile time.

How do I pick a random value from an enum?

By I Wayan Saryada in Basic, Core API 6 Comments

The following code snippet will show you how to pick a random value from an enum. First we’ll create an enum called BaseColor which will have three valid value. These values are Red, Green and Blue.

To allow us to get random value of this BaseColor enum we define a getRandomColor() method in the enum. This method use the java.util.Random to create a random value. This random value then will be used to pick a random value from the enum.

Let’s see the code snippet below:

package org.kodejava.basic;

import java.util.Random;

public class EnumGetRandomValueExample {
    public static void main(String[] args) {
        // Pick a random BaseColor for 10 times.
        for (int i = 0; i < 10; i++) {
            System.out.printf("color[%d] = %s%n", i,
                    BaseColor.getRandomColor());
        }
    }

    /**
     * BaseColor enum.
     */
    private enum BaseColor {
        Red,
        Green,
        Blue;

        /**
         * Pick a random value of the BaseColor enum.
         *
         * @return a random BaseColor.
         */
        public static BaseColor getRandomColor() {
            Random random = new Random();
            return values()[random.nextInt(values().length)];
        }
    }
}

The output of the code snippet:

color[0] = Green
color[1] = Green
color[2] = Blue
color[3] = Red
color[4] = Blue
color[5] = Blue
color[6] = Blue
color[7] = Blue
color[8] = Green
color[9] = Blue

How do I copy a file in JDK 7?

By I Wayan Saryada in Core API, IO 0 Comment

In this example you’ll see how to copy a file using the new API provided in the JDK 7. The first step is to define the source and the target of the file to be copied. For this we can use the Path class. To create an instance of Path we use the Paths.get() method by passing the path information as the arguments.

Next we can configure the file copy operation option. For this we can define it as an array of CopyOtion. We can use copy option such as StandardCopyOption.REPLACE_EXISTING and StandardCopyOption.COPY_ATTRIBUTES.

Finally, to copy the file we use the Files.copy() method. We give three arguments to this method, they are the source file, the target file and the copy options information.

Let’s see the code snippet below:

package org.kodejava.io;

import java.io.IOException;
import java.nio.file.*;

public class NioFileCopyDemo {
    public static void main(String[] args) {
        // Define the source and target of the file to be copied.
        Path source = Paths.get("D:/resources/data.txt");
        Path target = Paths.get("D:/resources/data.bak");

        // Define the options used in the file copy process.
        CopyOption[] options = new CopyOption[]{
                StandardCopyOption.REPLACE_EXISTING,
                StandardCopyOption.COPY_ATTRIBUTES
        };

        try {
            // Copy file from source to target using the defined 
            // configuration.
            Files.copy(source, target, options);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I split a string with multiple spaces?

By I Wayan Saryada in Core API, Lang Package 3 Comments

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.lang;

import java.util.Arrays;

public class SplitStringMultiSpaces {
    public static void main(String[] args) {
        String text = "04/11/2021    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  = [04/11/2021, SHOES, RUNNING, RED, 99.9, USD]

How do I clear the content of an array?

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

In this example you’ll learn how to clear or reset the content of an array. We can use the java.util.Arrays.fill() method to replace to content of each element in the array. In the example below we create two arrays, names and numbers array. We initialize these arrays with some values and then clear the value by assigning null to each element of the array using the Arrays.fill() method.

package org.kodejava.util;

import java.util.Arrays;

public class ArrayClear {
    public static void main(String[] args) {
        String[] names = {"Alice", "Bob", "Carol"};
        System.out.println("Names = " + Arrays.toString(names));

        // Replace the contents of the names array to null for each array
        // element.
        Arrays.fill(names, null);
        System.out.println("Names = " + Arrays.toString(names));

        Integer[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        System.out.println("Numbers = " + Arrays.toString(numbers));

        // Replace the contents of the numbers array to null for each
        // array element.
        Arrays.fill(numbers, null);
        System.out.println("Numbers = " + Arrays.toString(numbers));
    }
}

The output of the code snippet:

Names = [Alice, Bob, Carol]
Names = [null, null, null]
Numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Numbers = [null, null, null, null, null, null, null, null, null, null]