How do I get all available Locale language codes?

By Wayan in Core API, Util Package 0 Comment

When you want to internationalize your application, you need to know the language code and country code. These codes will be used as the properties file name (the file name must be ended in language_COUNTRY.properties). Here is an example that show how to get all supported language’s code.

package org.kodejava.util;

import java.util.Locale;

public class LocaleCountryLanguageCode {
    public static void main(String[] args) {
        // Gets an array of all installed locales. The returned array represents
        // the union of locales supported by the Java runtime environment and by 
        // installed LocaleServiceProvider implementations.
        Locale[] locales = Locale.getAvailableLocales();

        for (Locale locale : locales) {
            System.out.printf("Locale name: %s = %s_%s%n",
                    locale.getDisplayName(), locale.getLanguage(), locale.getCountry());
        }
    }
}

Here are some of the results produces by the code above:

...
Locale name: Kikuyu (Latin, Kenya) = ki_KE
Locale name: Spanish (Brazil) = es_BR
Locale name: Koyra Chiini (Mali) = khq_ML
Locale name: English (Solomon Islands) = en_SB
Locale name: Tibetan (Tibetan, China) = bo_CN
Locale name: Cherokee (United States) = chr_US
Locale name: Kinyarwanda (Rwanda) = rw_RW
Locale name: Tachelhit (Tifinagh, Morocco) = shi_MA
Locale name: Arabic (Iraq) = ar_IQ
Locale name: Nyankole = nyn_
...

How do I select records from database using JdbcTemplate?

By Wayan in Spring JDBC 0 Comment

In this example you will learn how to select records from the database using JdbcTemplate.queryForList() method. This method returns a List object which stores information selected from the table in a HashMap object. The key of the map is the table’s field names while the value of the map contains the corresponding table’s field value.

package org.kodejava.spring.jdbc;

import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.datasource.DriverManagerDataSource;

import java.util.List;
import java.util.Map;

public class SelectDemo {
    public static void main(String[] args) {
        // Creates a DataSource object.
        DriverManagerDataSource ds = new DriverManagerDataSource();
        ds.setDriverClassName("com.mysql.cj.jdbc.Driver");
        ds.setUrl("jdbc:mysql://localhost/musicdb");
        ds.setUsername("root");
        ds.setPassword("");

        // Creates an instance of JdbcTemplate.
        JdbcTemplate template = new JdbcTemplate(ds);

        // Executes a select query using queryForList() method. This
        // method returns a List containing HashMap object. The key
        // of the map is the table's field name and the value is
        // the table's field value.
        String query = "SELECT * FROM record";
        List<Map<String, Object>> results = template.queryForList(query);
        for (Map<String, Object> result : results) {
            for (String key : result.keySet()) {
                System.out.print(key + " = " + result.get(key) + "; ");
            }
            System.out.println();
        }

    }
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>6.1.10</version>
    </dependency>
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <version>8.4.0</version>
    </dependency>
</dependencies>

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How do I delete records from database using JdbcTemplate?

By Wayan in Spring JDBC 0 Comment

The code below demonstrates on how to delete some records from database using the JdbcTemplate.

package org.kodejava.spring.jdbc;

import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.datasource.DriverManagerDataSource;

import javax.sql.DataSource;

public class DeleteDemo {
    public static final String DRIVER = "com.mysql.cj.jdbc.Driver";
    public static final String URL = "jdbc:mysql://localhost/musicdb";
    public static final String USERNAME = "root";
    public static final String PASSWORD = "";

    public static final String QUERY = "DELETE FROM record WHERE id = ?";

    private final DataSource dataSource;

    public DeleteDemo(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    /**
     * Returns a DataSource object.
     *
     * @return a DataSource.
     */
    public static DataSource getDataSource() {
        DriverManagerDataSource ds = new DriverManagerDataSource();
        ds.setDriverClassName(DeleteDemo.DRIVER);
        ds.setUrl(DeleteDemo.URL);
        ds.setUsername(DeleteDemo.USERNAME);
        ds.setPassword(DeleteDemo.PASSWORD);
        return ds;
    }

    public static void main(String[] args) {
        DataSource ds = getDataSource();
        DeleteDemo demo = new DeleteDemo(ds);

        Long id = 1L;
        demo.deleteRecord(id);
    }

    public void deleteRecord(Long id) {
        // Creates an instance of JdbcTemplate and supply a data
        // source object.
        JdbcTemplate template = new JdbcTemplate(this.dataSource);

        // Delete a record from database where the record
        // id matches with the specified parameter.
        Object[] params = {id};
        int rows = template.update(DeleteDemo.QUERY, params);
        System.out.println(rows + " row(s) deleted.");
    }
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>6.1.10</version>
    </dependency>
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <version>8.4.0</version>
    </dependency>
</dependencies>

Maven Central Maven Central

How do I update records in the database using JdbcTemplate?

By Wayan in Spring JDBC 0 Comment

The example demonstrated below will show you how to use the JdbcTemplate.update() method for updating records in database. This method returns an integer value indicating number of records updated in the database when the query is executed.

package org.kodejava.spring.jdbc;

import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.datasource.DriverManagerDataSource;

import javax.sql.DataSource;
import java.sql.Types;
import java.util.Date;

public class UpdateDemo {
    public static final String DRIVER = "com.mysql.cj.jdbc.Driver";
    public static final String URL = "jdbc:mysql://localhost/musicdb";
    public static final String USERNAME = "root";
    public static final String PASSWORD = "";

    public static final String QUERY =
            "UPDATE record SET title = ?, release_date = ? WHERE id = ?";

    private final DataSource dataSource;

    public UpdateDemo(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    public static void main(String[] args) {
        DataSource ds = getDataSource();
        UpdateDemo demo = new UpdateDemo(ds);

        Long id = 2L;
        String title = "The Beatles 1967 - 1970";
        Date releaseDate = new Date();
        demo.updateRecord(id, title, releaseDate);
    }

    /**
     * Returns a data source object.
     *
     * @return a DataSource.
     */
    public static DataSource getDataSource() {
        DriverManagerDataSource ds = new DriverManagerDataSource();
        ds.setDriverClassName(UpdateDemo.DRIVER);
        ds.setUrl(UpdateDemo.URL);
        ds.setUsername(UpdateDemo.USERNAME);
        ds.setPassword(UpdateDemo.PASSWORD);
        return ds;
    }

    public void updateRecord(Long id, String title, Date releaseDate) {
        // Creates an instance of JdbcTemplate and set the DataSource.
        // We can use the template update() method to update records
        // in the database. Below we use an update() method that accepts
        // three parameters: the sql query, the parameter values and
        // the parameter data types.
        JdbcTemplate template = new JdbcTemplate(this.dataSource);

        Object[] params = {title, releaseDate, id};
        int[] types = {Types.VARCHAR, Types.DATE, Types.BIGINT};

        int rows = template.update(UpdateDemo.QUERY, params, types);
        System.out.println(rows + " row(s) updated.");
    }
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>6.1.10</version>
    </dependency>
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <version>8.4.0</version>
    </dependency>
</dependencies>

Maven Central Maven Central

How do I use the SortedMap interface?

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

import java.util.*;

public class SortedMapDemo {
    public static void main(String[] args) {
        SortedMap<String, String> sorted = new TreeMap<>();
        sorted.put("United States", "New York");
        sorted.put("United Kingdom", "London");
        sorted.put("Netherlands", "Amsterdam");
        sorted.put("Japan", "Tokyo");
        sorted.put("France", "Paris");

        // Gets the first(lowest) key currently in this map
        String firstKey = sorted.firstKey();

        // Gets the last (highest) key currently in this map
        String lastKey = sorted.lastKey();

        System.out.println("First key: " + firstKey);
        System.out.println("Last key : " + lastKey);

        // Gets a view of the portion of this map whose keys range
        // from fromKey(Japan), inclusive, to toKey(United Kingdom),
        // exclusive. (If fromKey and toKey are equal, the returned
        // map is empty.)
        SortedMap<String, String> sub = sorted.subMap("Japan",
                "United Kingdom");
        Set<String> subKeys = sub.keySet();
        System.out.println("\nSub Map: ");
        System.out.println("============");
        for (String key : subKeys) {
            System.out.println(key);
        }

        // Gets a view of the portion of this map whose keys are
        // strictly less than toKey(in this example is Netherlands)
        SortedMap<String, String> head = sorted.headMap("Netherlands");
        Set<String> headKeys = head.keySet();
        System.out.println("\nHead Map:");
        System.out.println("============");
        for (String key : headKeys) {
            System.out.println(key);
        }

        // Gets a view of the portion of this map whose keys are
        // strictly greater than or equal fromKey(in this example
        // is Netherlands)
        SortedMap<String, String> tail = sorted.tailMap("Netherlands");
        Set<String> tailKeys = tail.keySet();
        System.out.println("\nTail Map:");
        System.out.println("============");
        for (String key : tailKeys) {
            System.out.println(key);
        }
    }
}

Here is the output of the program:

First key: France
Last key : United States

Sub Map: 
============
Japan
Netherlands

Head Map:
============
France
Japan

Tail Map:
============
Netherlands
United Kingdom
United States

How do I convert a java.util.Vector into an array?

By Wayan in Core API, Util Package 0 Comment

This example demonstrates how to convert a Vector object into an array. You can use the Vector.copyInto(Object[] array) method to create a copy of the Vector object in array form.

package org.kodejava.util;

import java.util.Vector;

public class VectorToArray {
    public static void main(String[] args) {
        Vector<Integer> vector = new Vector<>();
        vector.add(10);
        vector.add(20);
        vector.add(30);
        vector.add(40);
        vector.add(50);

        // Declares and initializes an Integer array.
        Integer[] numbers = new Integer[vector.size()];

        // Copies the components of this vector into the specified
        // array of Integer
        vector.copyInto(numbers);

        for (Integer number : numbers) {
            System.out.println("Number: " + number);
        }
    }
}

The result of the code snippet above:

Number: 10
Number: 20
Number: 30
Number: 40
Number: 50

How do I use the shift right “>>” operator?

By Wayan in Basic, Core API 0 Comment

The signed shift right operator >> shifts a bit pattern to the right. This operator operates with two operand, the left-hand operand to be shifted and the right-hand operand tells how much position to shift.

Shifting a 1000 bit pattern using the >> operator 2 position will produce a 0010 bit pattern. The signed shift right operator produce a result that equals to dividing a number by 2.

package org.kodejava.basic;

public class SignedRightShiftOperator {
    public static void main(String[] args) {
        // The binary representation of 32 is
        // "00000000000000000000000000100000"
        int number = 32;
        System.out.println("number       = " + number);
        System.out.println("binary       = " +
                Integer.toBinaryString(number));

        // Using the shift right operator we shift the bits
        // four times to the right which resulting the result
        // of "00000000000000000000000000000010"
        int shiftedRight = number >> 4;
        System.out.println("shiftedRight = " + shiftedRight);
        System.out.println("binary       = " +
                Integer.toBinaryString(shiftedRight));
    }
}

The result of the code snippet:

number       = 32
binary       = 100000
shiftedRight = 2
binary       = 10

How do I use the shift left “<<" operator?

By Wayan in Basic, Core API 2 Comments

The signed shift left operator << shifts a bit pattern to the left. This operator operates with two operand, the left-hand operand to be shifted and the right-hand operand tells how much position to shift.

Shifting a 0010 bit pattern using the << operator 2 position will produce a 1000 bit pattern. The signed shift left operator produce a result that equals to multiplying a number by 2, which double the value of a number.

package org.kodejava.basic;

public class SignedLeftShiftOperator {
    public static void main(String[] args) {
        // The binary representation of 2 is "0010"
        int number = 2;
        System.out.println("number      = " + number);
        System.out.println("binary      = " +
                Integer.toBinaryString(number));

        // Using the shift left operator we shift the bits two
        // times to the left. This will shift the "0010" into
        // "1000"
        int shiftedLeft = number << 2;
        System.out.println("shiftedLeft = " + shiftedLeft);
        System.out.println("binary      = " +
                Integer.toBinaryString(shiftedLeft));
    }
}

The result of the code snippet:

number      = 2
binary      = 10
shiftedLeft = 8
binary      = 1000

How do I use the unary bitwise complement “~” operator?

By Wayan in Basic, Core API 0 Comment

The unary bitwise complement operator (~) inverts a bit pattern; it can be applied to any of the integral types, making every 0 a 1 and every 1 a 0.

For example, an integer contains 32 bits; applying this operator to a value whose bit pattern is 00000000000000000000000000001000 would change its pattern to 11111111111111111111111111110111.

package org.kodejava.basic;

public class UnaryBitwiseComplementOperator {
    public static void main(String[] args) {
        // An integer type contains 32 bit information.
        // 8 = 00000000000000000000000000001000
        int number = 8;
        System.out.println("number = " + number);
        System.out.println(Integer.toBinaryString(number));

        // Using the ~ operator inverts the number by change the
        // every "0" to "1" and every "1" to "0".
        // 00000000000000000000000000001000
        // 11111111111111111111111111110111
        //
        int invertedNumber = ~number;
        System.out.println("invertedNumber = " + invertedNumber);
        System.out.println(Integer.toBinaryString(invertedNumber));
    }
}

The result of the code snippet:

number = 8
1000
invertedNumber = -9
11111111111111111111111111110111

How do I remove elements from Deque?

By Wayan in Core API, Util Package 0 Comment

This example shows you how to remove some elements from the Deque object. We can use the following methods for removing elements from Deque: remove(), remove(Object o), removeFirst(), removeLast().

package org.kodejava.util;

import java.util.Deque;
import java.util.LinkedList;

public class RemoveDequeDemo {
    public static void main(String[] args) {
        Deque<String> deque = new LinkedList<>();
        deque.add("A");
        deque.add("B");
        deque.add("C");
        deque.add("D");
        deque.add("E");
        deque.add("F");

        // Removes and retrieves the head of this Deque
        deque.remove();      // Removes "A"

        // Removes the first occurrence of element from this Deque
        deque.remove("F");   // Removes "F"

        // Retrieves and removes the first element of this deque
        deque.removeFirst(); // Removes "B"

        // Retrieves and removes the last element of this deque
        deque.removeLast();  // Removes "E"

        for (String item : deque) {
            System.out.println("Item = " + item);
        }
    }
}