Kode Java - Learn Java by Examples

How do I convert double value into int value?

By Wayan in Basic, Core API Last modified: May 27, 2023 0 Comment

To convert double value into an int value we can use type casting or using the Double.intValue() method call. The code snippet below show you how to do it.

package org.kodejava.basic;

public class DoubleToInt {
    public static void main(String[] args) {
        Double numberA = 49.99;
        System.out.println("numberA = " + numberA);

        // Converting Double value to int value by calling
        // the Double.intValue() method.
        int numberB = numberA.intValue();
        System.out.println("numberB = " + numberB);

        // Converting Double value to int value by casting
        // the primitive double value of the Double instance
        int numberC = (int) numberA.doubleValue();
        System.out.println("numberC = " + numberC);

        double numberD = 99.99;
        System.out.println("numberD = " + numberD);

        // Converting double value into int value using
        // type casting
        int numberE = (int) numberD;
        System.out.println("numberE = " + numberE);
    }
}

How do I call a stored procedure that return a result set?

By Wayan in JDBC Last modified: May 31, 2024 0 Comment

This example show you how to call a stored procedure that return a result set of the query execution result.

package org.kodejava.jdbc;

import java.math.BigDecimal;
import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;

public class CallableStatementExample {
    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)) {

            // Prepares a call to the stored procedure. This stored procedure takes
            // one IN parameter
            String query = "call Get_Product_By_Price(?)";
            CallableStatement cb = connection.prepareCall(query);

            // Sets the input parameter
            cb.setBigDecimal(1, new BigDecimal("50.39"));

            // Execute the query
            ResultSet rs = cb.executeQuery();

            while (rs.next()) {
                System.out.println("Product: " + rs.getString(1));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Here is the stored procedure script we use in the example above.

DELIMITER ;;
DROP PROCEDURE IF EXISTS Get_Product_By_Price;;
CREATE PROCEDURE Get_Product_By_Price(IN product_price DECIMAL(10, 2))
BEGIN
    SELECT name FROM product WHERE price = product_price;
END;;
DELIMITER ;

Maven dependencies

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

How do I register out parameter in CallableStatement?

By Wayan in JDBC Last modified: May 31, 2024 0 Comment

This example show you how to register out parameter for executing a stored procedure using the CallableStatement.registerOutParameter() method call. We must register the out parameters before the query execution. The registerOutParameter() method takes two parameters, the index of the parameter and the sql data type of the out parameter.

package org.kodejava.jdbc;

import java.sql.*;

public class RegisterOutParameter {
    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)) {

            // Creates a CallableStatement for executing the stored
            // procedure
            String query = "call Get_Product_Detail_By_Name(?, ?, ?)";
            CallableStatement cb = connection.prepareCall(query);

            // Sets the input parameter
            cb.setString(1, "Data Structures, Algorithms");

            // Registers the out parameters
            cb.registerOutParameter(2, Types.VARCHAR);
            cb.registerOutParameter(3, Types.DECIMAL);

            // Executes the query
            cb.executeQuery();

            // Gets the query result output
            System.out.println("Name  : " + cb.getString(1));
            System.out.println("Code  : " + cb.getString(2));
            System.out.println("Price : " + cb.getBigDecimal(3));
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Here is the MySQL stored procedure that we call in the code above.

DELIMITER ;;
DROP PROCEDURE IF EXISTS `Get_Product_Detail_By_Name`;;
CREATE PROCEDURE `Get_Product_Detail_By_Name`(
    INOUT product_name VARCHAR(100),
    OUT product_code VARCHAR(20),
    OUT product_price DECIMAL(10, 2))
BEGIN
    SELECT code INTO product_code FROM product WHERE name = product_name;

    SELECT price INTO product_price FROM product WHERE name = product_name;
END;;
DELIMITER ;

Maven Dependencies

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

How do I use the unary operators?

By Wayan in Basic, Core API Last modified: May 27, 2023 0 Comment

The unary operators requires only one operand to operate on, it can perform operations such as incrementing or decrementing value by one, negating a value or inverting a value of a boolean expression.

The unary operators use the following symbols:

Symbol	Description
`+`	unary plus operator; indicates positive value
`-`	unary minus operator; negates a value
`++`	unary increment operator; increments value by one
`--`	unary decrement operator; decrements value by one
`!`	unary logical complement operator; inverts a boolean value

package org.kodejava.basic;

public class UnaryOperatorsDemo {
    public static void main(String[] args) {
        int result = +10;  // result = 10
        System.out.println("result = " + result);
        result--;          // result = 9
        System.out.println("result = " + result);
        result++;          // result = 10
        System.out.println("result = " + result);
        result = -result;  // result = -10;
        System.out.println("result = " + result);

        // The increment and decrement operators can be applied
        // before (prefix) or after (postfix) the operand. Both
        // of them will increment or decrement value by one. The
        // different is that the prefix version evaluates to the
        // incremented or decremented value while the postfix
        // version evaluates to the original value;
        --result;
        System.out.println("result = " + result);
        ++result;
        System.out.println("result = " + result);

        boolean status = result == -10;  // status = true
        System.out.println("status = " + status);
        status = !status;                // status = false;
        System.out.println("status = " + status);
    }
}

How do I use the arithmetic operators?

By Wayan in Basic, Core API Last modified: May 27, 2023 0 Comment

The following example show you how to use Java arithmetic operators. The operators consist of the multiplicative operators (* for multiplication, / for division), % for remainder of division) and the additive operators (+ for addition,- for subtraction).

You’ll also see we are using a combination of a simple assignment operator with the arithmetic operators to create compound assignments.

package org.kodejava.basic;

public class ArithmeticOperatorsDemo {
    public static void main(String[] args) {
        int result = 5 + 4;  // result = 9
        System.out.println("result = " + result);

        result = result - 2; // result = 7
        System.out.println("result = " + result);

        result = result * 4; // result = 28
        System.out.println("result = " + result);

        result = result / 7; // result = 4
        System.out.println("result = " + result);

        result = result % 3; // result = 1
        System.out.println("result = " + result);

        // Combining the arithmetic operators with a simple assignment
        // operators give us a compound assignment. We can write the
        // operation above in the following form. But as you can see
        // the above snippets is easier to read.
        result = 5 + 4; // result = 9
        System.out.println("result = " + result);

        result -= 2;    // result = 7
        System.out.println("result = " + result);

        result *= 4;    // result = 28
        System.out.println("result = " + result);

        result /= 7;    // result = 4
        System.out.println("result = " + result);

        result %= 3;    // result = 1
        System.out.println("result = " + result);
    }
}

How do I set the query timeout limit?

By Wayan in JDBC Last modified: May 31, 2024 1 Comment

The Statement.setQueryTimeout() method set the limit in seconds for query execution time. The execution has no timeout limit when the value is set to zero.

package org.kodejava.jdbc;

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

public class QueryTimeout {
    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 stmt = connection.createStatement();

            // Sets the number of seconds the driver will wait for
            // a statement object to execute to the given number of
            // seconds. If the limit is exceeded, an SQLException
            // is thrown.
            stmt.setQueryTimeout(60);

            // Execute sql query
            ResultSet rs = stmt.executeQuery("select * from product");

            while (rs.next()) {
                System.out.println("code: " + rs.getString("code") + 
                                   ", product: " + rs.getString("name") + 
                                   ", price: " + rs.getDouble("price"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

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

How do I get peak live threads count?

By Wayan in Core API, Management Last modified: May 27, 2023 0 Comment

package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;

public class PeakThreadCount {
    public static void main(String[] args) {
        // Get the managed bean for the thread system of the Java
        // virtual machine.
        ThreadMXBean bean = ManagementFactory.getThreadMXBean();

        // Get the peak live thread count since the Java virtual
        // machine started or peak was reset.
        int peakThreadCount = bean.getPeakThreadCount();
        System.out.println("Peak Thread Count = " + peakThreadCount);
    }
}

How do I get current number of live threads?

By Wayan in Core API, Management Last modified: May 27, 2023 0 Comment

package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;

public class ThreadCount {

    public static void main(String[] args) {
        // Get the managed bean for the thread system of the Java
        // virtual machine.
        ThreadMXBean bean = ManagementFactory.getThreadMXBean();

        // Get the current number of live threads including both
        // daemon and non-daemon threads.
        int threadCount = bean.getThreadCount();
        System.out.println("Thread Count = " + threadCount);
    }
}

How do I get the Java classpath?

By Wayan in Core API, Management Last modified: May 27, 2023 0 Comment

The RuntimeMXBean.getClassPath() returns the Java class path that is used by the system class loader to search for class files. This method is equivalent to System.getProperty("java.class.path").

Multiple paths in the Java class path are separated by the path separator character of the platform of the Java virtual machine being monitored.

package org.kodejava.lang.management;

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

public class GetClassPath {
    public static void main(String[] args) {
        RuntimeMXBean bean = ManagementFactory.getRuntimeMXBean();
        String classPath = bean.getClassPath();
        System.out.println("ClassPath = " + classPath);
    }
}

How do I get system properties information?

By Wayan in Core API, Management Last modified: May 27, 2023 0 Comment

package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.util.Map;
import java.util.Set;

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

        // Returns a map of names and values of all system
        // properties. This method calls System.getProperties()
        // to get all system properties. Properties whose
        // name or value is not a String are omitted.
        Map<String, String> systemProperties = bean.getSystemProperties();
        Set<String> keys = systemProperties.keySet();
        for (String key : keys) {
            String value = systemProperties.get(key);
            System.out.printf("Property[%s] = %s%n", key, value);
        }
    }
}

Some properties produced by the code snippet above are:

Property[java.specification.version] = 17
Property[sun.cpu.isalist] = amd64
Property[sun.jnu.encoding] = Cp1252
Property[java.vm.vendor] = Oracle Corporation
Property[sun.arch.data.model] = 64
Property[user.variant] = 
Property[java.vendor.url] = https://java.oracle.com/
...
...
Property[java.vm.info] = mixed mode, sharing.
Property[java.vendor] = Oracle Corporation.
Property[java.vm.version] = 17+35-LTS-2724.
Property[sun.io.unicode.encoding] = UnicodeLittle.
Property[java.class.version] = 61.0.