How do I get the start time of a JVM?

By I Wayan Saryada in Core API, Management 0 Comment 
package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.util.Date;

public class GetStartTime {
    public static void main(String[] args) {
        RuntimeMXBean bean = ManagementFactory.getRuntimeMXBean();

        // Returns the start time of the Java virtual machine in 
        // milliseconds. This method returns the approximate time 
        // when the Java virtual machine started.
        long startTime = bean.getStartTime();
        Date startDate = new Date(startTime);
        System.out.println("Start Time = " + startTime);
        System.out.println("Start Date = " + startDate);
    }
}

The result of the code snippet above:

Start Time = 1634391703196
Start Date = Sat Oct 16 21:41:43 CST 2021

How do I get the uptime of a JVM?

By I Wayan Saryada in Core API, Management 0 Comment

The following code snippet demonstrates how to get the time for how long has the JVM been running.

package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;

public class GetUptime {
    public static void main(String[] args) {
        RuntimeMXBean bean = ManagementFactory.getRuntimeMXBean();

        // Returns the uptime of the Java virtual machine in
        // milliseconds.
        long uptime = bean.getUptime();
        System.out.printf("Uptime = %d (ms).", uptime);
    }
}

The output of the code snippet above:

Uptime = 125 (ms).

How do I limit MySQL query result?

By I Wayan Saryada in JDBC 0 Comment 
package org.kodejava.jdbc;

import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class SqlLimitExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Create PreparedStatement to get all data from a database.
            String query = "select count(*) from product";
            PreparedStatement ps = connection.prepareStatement(query);
            ResultSet result = ps.executeQuery();

            int total = 0;
            while (result.next()) {
                total = result.getInt(1);
            }

            System.out.println("Total number of data in database: " +
                               total + "\n");

            // Create PreparedStatement to the first 5 records only.
            query = "select * from product limit 5";
            ps = connection.prepareStatement(query);
            result = ps.executeQuery();

            System.out.println("Result fetched with specified limit 5");
            System.out.println("====================================");
            while (result.next()) {
                System.out.println("id:" + result.getInt("id") +
                                   ", code:" + result.getString("code") +
                                   ", name:" + result.getString("name") +
                                   ", price:" + result.getString("price"));
            }

            // Create PreparedStatement to get data from the 4th
            // record (remember the first record is 0) and limited
            // to 3 records only.
            query = "select * from product limit 3, 3";
            ps = connection.prepareStatement(query);
            result = ps.executeQuery();

            System.out.println("\nResult fetched with specified limit 3, 3");
            System.out.println("====================================");
            while (result.next()) {
                System.out.println("id:" + result.getInt("id") +
                                   ", code:" + result.getString("code") +
                                   ", name:" + result.getString("name") +
                                   ", price:" + result.getString("price"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

An example result of our program is:

Total number of data in database: 9

Result fetched with specified limit 5
====================================
id:1, code:P0000001, name:UML Distilled 3rd Edition, price:25.00
id:3, code:P0000003, name:PHP Programming, price:20.00
id:4, code:P0000004, name:Longman Active Study Dictionary, price:40.00
id:5, code:P0000005, name:Ruby on Rails, price:24.00
id:6, code:P0000006, name:Championship Manager, price:0.00

Result fetched with specified limit 3, 3
====================================
id:5, code:P0000005, name:Ruby on Rails, price:24.00
id:6, code:P0000006, name:Championship Manager, price:0.00
id:7, code:P0000007, name:Transport Tycoon Deluxe, price:0.00

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Maven Central

How do I append and replace content of a StringBuffer?

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

A StringBuffer is like a String, but can be modified. StringBuffer are safe for use by multiple threads. The methods are synchronized where necessary so that all the operations on any particular instance behave as if they occur in some serial order that is consistent with the order of the method calls made by each of the individual threads involved.

As of release JDK 1.5, this class has been supplemented with an equivalent class designed for use by a single thread, the StringBuilder. The StringBuilder class should generally be used in preference to this one, as it supports all the operations, but it is faster, as it performs no synchronization.

package org.kodejava.lang;

public class StringBufferAppendReplace {
    public static void main(String[] args) {
        StringBuffer quote = new StringBuffer("an apple ");
        char a = 'a';
        String day = " day";
        StringBuffer sentences = new StringBuffer(" keep the doctor away");

        // Append a character into StringBuffer
        quote.append(a);
        System.out.println("quote = " + quote);

        // Append a string into StringBuffer
        quote.append(day);
        System.out.println("quote = " + quote);

        // Append another StringBuffer
        quote.append(sentences);
        System.out.println("quote = " + quote);

        // Replace a sub string from StringBuffer starting
        // from index = 3 to index = 8
        quote.replace(3, 8, "orange");
        System.out.println("quote = " + quote);
    }
}

Here is our program output:

quote = an apple a
quote = an apple a day
quote = an apple a day keep the doctor away
quote = an orange a day keep the doctor away

How do I set the fetch size of a statement?

By I Wayan Saryada in JDBC 0 Comment

Fetch size is the number of rows that should be fetched from the database on a single database network trip. When more rows are needed, another request is sent by the application to the database server.

Setting the correct fetch size will help our program to perform better by reducing the network communication generated between the program and the database server.

package org.kodejava.jdbc;

import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class SetFetchSizeExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            Statement statement = connection.createStatement();

            // Set the fetch size to 100.
            statement.setFetchSize(100);

            // Execute the given sql query
            String q = "select id, code, name, price from product";
            ResultSet rs = statement.executeQuery(q);

            while (rs.next()) {
                System.out.println("id:" + rs.getLong("id") +
                                   ", code:" + rs.getString("code") +
                                   ", name:" + rs.getString("name") +
                                   ", price:" + rs.getString("price"));
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Example result of the code snippet above is:

id:1, code:P0000001, name:UML Distilled 3rd Edition, price:25.00
id:3, code:P0000003, name:PHP Programming, price:20.00
id:4, code:P0000004, name:Longman Active Study Dictionary, price:40.00
id:5, code:P0000005, name:Ruby on Rails, price:24.00
id:6, code:P0000006, name:Championship Manager, price:0.00
id:7, code:P0000007, name:Transport Tycoon Deluxe, price:0.00
id:8, code:P0000008, name:Roller Coaster Tycoon 3, price:0.00
id:9, code:P0000009, name:Pro Evolution Soccer, price:0.00
id:10, code:P0000010, name:Data Structures, Algorithms, price:50.99

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Maven Central