How do I clear system property?

By Wayan in Core API, Lang Package 0 Comment

The System.clearProperty(String key) method enables you to remove a system property. The key must not be an empty string or a null value because it will cause the method to throw an IllegalArgumentException or a NullPointerException.

It will also check if a SecurityManager exists and if you don’t have a write permission to the system property a SecurityException is going to be thrown.

package org.kodejava.lang;

public class ClearProperty {
    public static void main(String[] args) {
        String key = "user.dir";
        System.out.println(key + " = " + System.getProperty(key));

        // The System.clearProperty() method available since Java 1.5
        System.clearProperty(key);
        System.out.println(key + " = " + System.getProperty(key));
    }
}

The code snippet above give us the following output:

user.dir = F:\Wayan\Kodejava\kodejava-example
user.dir = null

How do I get file separator symbol?

By Wayan in Core API, Lang Package 0 Comment

Creating a program to be run on more than one platform such as Windows and Linux our program need to understand the difference between both platform. The simplest thing for instance is the file separator. Windows use "\" (backslash) while Linux use "/" (forward slash).

To avoid manual checking for the operating system we can get the file separator symbol from the system property using the file.separator key.

package org.kodejava.lang;

public class FileSeparatorExample {
    public static void main(String[] args) {
        // file.separator system property return the correct file 
        // separator for each different platform (Windows = \), 
        // (Linux = /)
        String dataFolder = System.getProperty("user.dir") +
                System.getProperty("file.separator") + "data";

        System.out.println("Data Folder = " + dataFolder);
    }
}

How do I get the name of a class?

By Wayan in Core API, Lang Package 0 Comment 
package org.kodejava.lang;

import java.util.Calendar;
import java.math.BigDecimal;

public class ClassName {
    public static void main(String[] args) {
        // Get the name of the classes below.
        Class<?> clazz = String.class;
        System.out.println("Class Name: " + clazz.getName());

        clazz = Calendar.class;
        System.out.println("Class Name: " + clazz.getName());

        clazz = BigDecimal.class;
        System.out.println("Class Name: " + clazz.getName());
    }
}

The result of the code snippet above are:

Class Name: java.lang.String
Class Name: java.util.Calendar
Class Name: java.math.BigDecimal

How do I know if a class object is an interface or a class?

By Wayan in Core API, Lang Package 0 Comment 
package org.kodejava.lang;

public class CheckForInterface {
    public static void main(String[] args) {
        // Checking whether Cloneable is an interface or class
        Class<?> clazz = Cloneable.class;
        boolean isInterface = clazz.isInterface();
        System.out.println(clazz.getName() + " is an interface = " + isInterface);

        // Checking whether String is an interface or class
        clazz = String.class;
        isInterface = clazz.isInterface();
        System.out.println(clazz.getName() + " is an interface = " + isInterface);
    }
}

java.lang.Cloneable is an interface = true
java.lang.String is an interface = false

How do I get interfaces implemented by a class?

By Wayan in Core API, Lang Package 0 Comment

The getClass().getInterfaces() method return an array of Class that represents the interfaces implemented by an object.

package org.kodejava.lang;

import java.util.Date;
import java.util.Calendar;

public class ClassInterfaces {
    public static void main(String[] args) {
        // Get an instance of Date class
        Date date = Calendar.getInstance().getTime();

        // Get all interfaces implemented by the java.util.Date class and
        // print their names.
        Class<?>[] interfaces = date.getClass().getInterfaces();
        for (Class<?> i : interfaces) {
            System.out.printf("Interface of %s = %s%n", date.getClass().getName(), i.getName());
        }

        // For the primitive type the interface will be an empty array.
        interfaces = char.class.getInterfaces();
        for (Class<?> i : interfaces) {
            System.out.printf("Interface of %s = %s%n", char.class.getName(), i.getName());
        }
    }
}

The java.util.Date class implements the following interfaces:

Interface of java.util.Date = java.io.Serializable
Interface of java.util.Date = java.lang.Cloneable
Interface of java.util.Date = java.lang.Comparable