How do I use Collectors.toList() method?

By Wayan in Stream API 0 Comment

The Collectors.toList() method is a convenient method in the java.util.stream.Collectors class that provides a Collector to accumulate input elements into a new List.

Here is a simple example of how to use Collectors.toList():

package org.kodejava.stream;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class CollectorsToList {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9);

        List<Integer> evenNumbers = numbers.stream()
                .filter(n -> n % 2 == 0)
                .collect(Collectors.toList());

        System.out.println(evenNumbers);
    }
}

Output:

[2, 4, 6, 8]

In this example, we create a stream of numbers and filter it to only include the even numbers. Then we collect the output into a List using Collectors.toList(). The result is a List<Integer> that only includes the even numbers.

Remember that collect is a terminal operation (meaning it triggers the processing of the data) and it returns a collection or other desired result type. In case of Collectors.toList(), the result is a List.

How can I insert an element in array at a given position?

By Wayan in Core API, Util Package 0 Comment

As we know an array in Java is a fixed-size object, once it created its size cannot be changed. So if you want to have a resizable array-like object where you can insert an element at a given position you can use a java.util.List object type instead.

This example will show you how you can achieve array insert using the java.util.List and java.util.ArrayList object. Let see the code snippet below.

package org.kodejava.util;

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

public class ArrayInsert {
    public static void main(String[] args) {
        // Creates an array of integer value and prints the original values.
        Integer[] numbers = new Integer[]{1, 1, 2, 3, 8, 13, 21};
        System.out.println("Original numbers: " +
                Arrays.toString(numbers));

        // Creates an ArrayList object and initialize its values with the entire
        // content of numbers array. We use the add(index, element) method to add
        // element = 5 at index = 4.
        List<Integer> list = new ArrayList<>(Arrays.asList(numbers));
        list.add(4, 5);

        // Converts back the list into array object and prints the new values.
        numbers = list.toArray(new Integer[0]);
        System.out.println("After insert    : " + Arrays.toString(numbers));
    }
}

In the code snippet above the original array of Integer numbers will be converted into a List, in this case we use an ArrayList, we initialized the ArrayList by passing all elements of the array into the list constructor. The Arrays.asList() can be used to convert an array into a collection type object.

Next we insert a new element into the List using the add(int index, E element) method. Where index is the insert / add position and element is the element to be inserted. After the new element inserted we convert the List back to the original array.

Below is the result of the code snippet above:

Original numbers: [1, 1, 2, 3, 8, 13, 21]
After insert    : [1, 1, 2, 3, 5, 8, 13, 21]

How do I reverse the order of array elements?

By Wayan in Core API, Util Package 0 Comment

In this code snippet you’ll learn how to reverse the order of array elements. To reverse to element order will be using the Collections.reverse() method. This method requires an argument with List type. Because of this we need to convert the array to a List type first. We can use the Arrays.asList() to do the conversion. And then we reverse it. To convert the List back to array we can use the Collection.toArray() method.

Let’s see the code snippet below:

package org.kodejava.util;

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

public class ArrayReverse {
    public static void main(String[] args) {
        // Creates an array of Integers and print it out.
        Integer[] numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8};
        System.out.println("Arrays.toString(numbers) = " +
                Arrays.toString(numbers));

        // Convert the int arrays into a List.
        List<Integer> numberList = Arrays.asList(numbers);

        // Reverse the order of the List.
        Collections.reverse(numberList);

        // Convert the List back to array of Integers
        // and print it out.
        numberList.toArray(numbers);
        System.out.println("Arrays.toString(numbers) = " +
                Arrays.toString(numbers));
    }
}

The output of the code snippet above is:

Arrays.toString(numbers) = [0, 1, 2, 3, 4, 5, 6, 7, 8]
Arrays.toString(numbers) = [8, 7, 6, 5, 4, 3, 2, 1, 0]

How do I inject collections using list element in Spring?

By Wayan in Spring Core 0 Comment

The following example show you how to use the <list> element to wire collection property. We can use it to wire property of either arrays or some implementation of java.util.Collection such as java.util.ArrayList.

For this example we will create a bean called Album that have a collection of Song beans in it. So here is our bean classes.

package org.kodejava.spring.core;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;

public class Album {
    private String title;
    private int year;
    private List<Song> songs = new ArrayList<>();
    private Map<String, Publisher> publisher = new HashMap<>();
    private Properties props = new Properties();

    public Album() {
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public void setSongs(List<Song> songs) {
        this.songs = songs;
    }

    public void setPublisher(Map<String, Publisher> publisher) {
        this.publisher = publisher;
    }

    public void setProps(Properties props) {
        this.props = props;
    }

    @Override
    public String toString() {
        return "Album{" +
                "title='" + title + '\'' +
                ", year=" + year +
                ", songs=" + songs +
                ", publisher=" + publisher +
                ", props=" + props +
                '}';
    }
}

package org.kodejava.spring.core;

public class Song {
    private String title;
    private String writer;

    public Song() {
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public void setWriter(String writer) {
        this.writer = writer;
    }

    @Override
    public String toString() {
        return "Song{" +
                "title='" + title + '\'' +
                ", writer='" + writer + '\'' +
                '}';
    }
}

package org.kodejava.spring.core;

public class Publisher {
    private String name;

    public Publisher() {
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Publisher{" +
                "name=" + name +
                '}';
    }
}

Here is the Spring configuration file, CollectionList.xml.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="song1" class="org.kodejava.spring.core.Song">
        <property name="title" value="I Saw Her Standing There" />
        <property name="writer" value="Beatles" />
    </bean>

    <bean id="song2" class="org.kodejava.spring.core.Song">
        <property name="title" value="Misery" />
        <property name="writer" value="Beatles" />
    </bean>

    <bean id="song3" class="org.kodejava.spring.core.Song">
        <property name="title" value="Anna (Go to Him)" />
        <property name="writer" value="Beatles" />
    </bean>


    <bean id="album" class="org.kodejava.spring.core.Album">
        <property name="title" value="Please Please Me" />
        <property name="year" value="1963" />
        <property name="songs">
            <list>
                <ref bean="song1" />
                <ref bean="song2" />
                <ref bean="song3" />
            </list>
        </property>
    </bean>

</beans>

The part of the configuration that wire the song collection is inside the album bean. You can see that we have a property name songs. This property has a <list> element that contains a couple <ref> elements referring to some Song type beans.

Now let’s run it with the following code:

package org.kodejava.spring.core;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class DemoList {
    public static void main(String[] args) {
        var context = new ClassPathXmlApplicationContext("collection-list.xml");

        Album album = (Album) context.getBean("album");
        System.out.println("Album = " + album);
        context.close();
    }
}

You’ll see the following output when you run the program:

Album = Album{title='Please Please Me', year=1963, songs=[Song{title='I Saw Her Standing There', writer='Beatles'}, Song{title='Misery', writer='Beatles'}, Song{title='Anna (Go to Him)', writer='Beatles'}], publisher={}, props={}}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>5.3.23</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>5.3.23</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context-support</artifactId>
        <version>5.3.23</version>
    </dependency>
</dependencies>

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How do I create ZapfDingbats List in iText?

By Wayan in iText PDF 0 Comment

This example show you how to use the com.itextpdf.text.ZapfDingbatsList class to create a ZapfDingbatsList list using the iText pdf library.

package org.kodejava.itextpdf;

import com.itextpdf.text.*;
import com.itextpdf.text.pdf.PdfWriter;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;

public class ZapfDingbatsListDemo {
    public static void main(String[] args) {
        Document doc = new Document();
        try {
            PdfWriter.getInstance(doc, new FileOutputStream("ZapfDingbats.pdf"));
            doc.open();

            // Create a ZapfDingbatsList with char number 50
            List zapf1 = new ZapfDingbatsList(50);
            zapf1.add(new ListItem("Item 1"));
            zapf1.add(new ListItem("Item 2"));
            zapf1.add(new ListItem("Item 3"));
            doc.add(zapf1);

            // Create a ZapfDingbatsList with char number 55 and indent
            // it by 30.
            List zapf2 = new ZapfDingbatsList(55, 30);
            zapf2.add(new ListItem("Item 1"));
            zapf2.add(new ListItem("Item 2"));
            zapf2.add(new ListItem("Item 3"));
            doc.add(zapf2);
        } catch (DocumentException | FileNotFoundException e) {
            e.printStackTrace();
        } finally {
            doc.close();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.13.3</version>
</dependency>

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