How do I convert double value into int value?

By Wayan in Basic, Core API 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 use the unary operators?

By Wayan in Basic, Core API 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 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 get peak live threads count?

By Wayan in Core API, Management 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 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 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 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.

How do I get the start time of a JVM?

By Wayan 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 Wayan 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 append and replace content of a StringBuffer?

By Wayan 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