How do I destroy a thread group?

By Wayan in Core API, Lang Package 0 Comment

You can destroy a thread group by using destroy() method of ThreadGroup class. It will cleans up the thread group and removes it from the thread group hierarchy. It’s not only destroy the thread group, but also all its subgroups.

The destroy() method is of limited use: it can only be called if there are no threads presently in the thread group.

package org.kodejava.lang;

public class ThreadGroupDestroy {
    public static void main(String[] args) {
        ThreadGroup root = new ThreadGroup("Root");
        ThreadGroup server = new ThreadGroup(root, "ServerGroup");
        ThreadGroup client = new ThreadGroup(root, "ClientGroup");

        // Destroy 'root' thread groups and all its subgroup
        // ('server' & 'client')
        root.destroy();

        // Check if 'root' group and its subgroups already destroyed
        if (root.isDestroyed()) {
            System.out.println("Root group is destroyed");
        }

        if (server.isDestroyed()) {
            System.out.println("Server group is destroyed");
        }

        if (client.isDestroyed()) {
            System.out.println("Client group is destroyed");
        }
    }
}

How to automatically close resources in JDBC?

By Wayan in JDBC 0 Comment

One thing that we need to do manually when programming using JDBC is to make sure to close all the resources that we use. All resources including the ResultSet, Statement and Connection must be closed. This will usually produce a lot of boilerplate code in our program.

Starting from JDBC 4.1, which is a part of Java 7, we can use the try-with-resources statement to automatically manage the resources that we use. This try statement closes the resources used when the block finishes its execution either normally or abruptly.

Here is an example that shows us how to use the try-with-resources statement.

package org.kodejava.jdbc;

import java.sql.*;

public class TryWithResourceJdbc {
    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 conn =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD);
             Statement stmt = conn.createStatement();
             ResultSet rs = stmt.executeQuery("SELECT * FROM product")) {

            while (rs.next()) {
                String code = rs.getString("code");
                String name = rs.getString("name");

                System.out.println("Code: " + code + "; Name: " + name);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

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

Maven Central

How do I use try-with-resources statement?

By Wayan in Basic, Core API 0 Comment

The try-with-resources statement is introduced in the Java 7. With this new statement we can simplify resource management in our program, also known as ARM (Automatic Resource Management).

This statement is a try statement that declares one or more resources. After the program finish with the resource, it must be closed. The try-with-resources ensures that each resource is closed and the end of the statement.

Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.

package org.kodejava.basic;

import java.io.*;
import java.nio.charset.StandardCharsets;

public class TryWithResourceExample {
    public static void main(String[] args) {
        try {
            TryWithResourceExample demo = new TryWithResourceExample();
            demo.printStream("F:/tmp/data.txt");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void printStream(String fileName) throws IOException {
        char[] buffer = new char[1024];

        try (InputStream is = new FileInputStream(fileName);
             Reader reader = new BufferedReader(
                     new InputStreamReader(is, StandardCharsets.UTF_8))) {

            while (reader.read(buffer) != -1) {
                System.out.println(buffer);
            }
        }
    }
}

How do I use string in switch statement?

By Wayan in Basic, Core API 0 Comment

Starting from Java 7 release you can now use a String in the switch statement. On the previous version we can only use constants type of byte, char, short, int (and their corresponding reference / wrapper type) or enum constants in the switch statement.

The code below give you a simple example on how the Java 7 extended to allow the use of String in switch statement.

package org.kodejava.basic;

public class StringInSwitchExample {
    public static void main(String[] args) {
        String day = "Sunday";
        switch (day) {
            case "Sunday":
                System.out.println("doSomething");
                break;
            case "Monday":
                System.out.println("doSomethingElse");
                break;
            case "Tuesday":
            case "Wednesday":
                System.out.println("doSomeOtherThings");
                break;
            default:
                System.out.println("doDefault");
                break;
        }
    }
}

How do I use multi-catch statement?

By Wayan in Core API, Lang Package 1 Comment

The multi-catch is a language enhancement feature introduces in the Java 7. This allows us to use a single catch block to handle multiple exceptions. Each exception is separated by the pipe symbol (|).

Using the multi-catch simplify our exception handling and also reduce code duplicates in the catch block. Let’s see an example below:

package org.kodejava.lang;

import java.io.IOException;
import java.sql.SQLException;

public class MultiCatchDemo {
    public static void main(String[] args) {
        MultiCatchDemo demo = new MultiCatchDemo();
        try {
            demo.callA();
            demo.callB();
            demo.callC();
        } catch (IOException | SQLException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    private void callA() throws IOException {
        throw new IOException("IOException");
    }

    private void callB() throws SQLException {
        throw new SQLException("SQLException");
    }

    private void callC() throws ClassNotFoundException {
        throw new ClassNotFoundException("ClassNotFoundException");
    }
}