How do I convert primitive boolean type into Boolean object?

By Wayan in Core API, Lang Package 0 Comment

The following code snippet demonstrate how to use the Boolean.valueOf() method to convert primitive boolean value or a string into Boolean object. This method will return the corresponding Boolean object of the given primitive boolean value.

When a string value is passed to this method it will return Boolean.TRUE when the string is not null, and the value is equal, ignoring case, to the string "true". Otherwise, it will return Boolean.FALSE object.

package org.kodejava.lang;

public class BooleanValueOfExample {
    public static void main(String[] args) {
        boolean b = true;
        Boolean bool = Boolean.valueOf(b);
        System.out.println("bool = " + bool);

        // Here we test the conversion, which is likely unnecessary. But
        // here is shown the boolean true is equals to Boolean.TRUE static
        // variable and of course you can guest the boolean false value is
        // equals to Boolean.FALSE
        if (bool.equals(Boolean.TRUE)) {
            System.out.println("bool = " + bool);
        }

        // On the line below we convert a string to Boolean, it returns
        // true if and only if the string is equals to "true" otherwise it
        // returns false
        String s = "false";
        Boolean bools = Boolean.valueOf(s);
        System.out.println("bools = " + bools);

        String f = "abc";
        Boolean abc = Boolean.valueOf(f);
        System.out.println("abc = " + abc);
    }
}

The code snippet will print the following output:

bool = true
bool = true
boolS = false
abc = false

Can I create a boolean variable from string?

By Wayan in Core API, Lang Package 0 Comment

To convert a string into boolean we can use the Boolean.parseBoolean(String) method. If we pass a non null value that equals to true, ignoring case, this method will return true value. Given other values it will return a false boolean value.

package org.kodejava.lang;

public class BooleanParseExample {
    public static void main(String[] args) {
        // Parsing string "true" will result boolean true
        boolean boolA = Boolean.parseBoolean("true");
        System.out.println("boolA = " + boolA);

        // Parsing string "TRUE" also result boolean true, as the
        // parsing method is case insensitive
        boolean boolB = Boolean.parseBoolean("TRUE");
        System.out.println("boolB = " + boolB);

        // The operation below will return false, as Yes is not
        // a valid string value for boolean expression
        boolean boolC = Boolean.parseBoolean("Yes");
        System.out.println("boolC = " + boolC);

        // Parsing a number is also not a valid expression so the
        // parsing method return false
        boolean boolD = Boolean.parseBoolean("1");
        System.out.println("boolD = " + boolD);
    }
}

The code snippet above will print the following output:

boolA = true
boolB = true
boolC = false
boolD = false

How do I delete a file in Java?

By Wayan in Core API, IO 0 Comment

In this example you will see how to delete a file in Java. To delete a file we start by creating a File object that represent the file to be deleted. We use the exists() method to check if the file is exists before we try to delete it.

To delete the file we call the delete() method of the File object. If the file was successfully deleted the method will return a boolean true result, otherwise it will return false. Let’s try the code snippet below.

package org.kodejava.io;

import java.io.File;

public class FileDeleteExample {
    public static void main(String[] args) {
        // When want to delete a file named readme.txt
        File file = new File("write.txt");

        // Checks if the file is exists before deletion.
        if (file.exists()) {
            System.out.println("Deleting " + file.getAbsolutePath());
            // Use the delete method to delete the given file.
            boolean deleted = file.delete();
            if (deleted) {
                System.out.println(file.getAbsolutePath() + " was deleted.");
            }
        } else {
            System.out.println(file.getAbsolutePath() + " not found.");
        }
    }
}

How do I get IP address of localhost?

By Wayan in Core API, Networking 0 Comment

The example here show you how to get an IP or host address using the java.net.InetAddress class. To get an instance of InetAddress we call a static method of this class, the method is getLocalHost(), which return the local host address. Next, to get the IP address we can call the getHostAddress() method.

package org.kodejava.net;

import java.net.InetAddress;
import java.net.UnknownHostException;

public class LocalHostIpAddress {
    public static void main(String[] args) {
        try {
            InetAddress address = InetAddress.getLocalHost();
            String ip = address.getHostAddress();

            System.out.println("IP Address = " + ip);
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
    }
}

The result of this code snippet:

IP Address = 30.30.30.60

How do I create an empty collection object?

By Wayan in Core API, Util Package 3 Comments

Sometimes you need to return an empty collection from your Java methods. The java.util.Collections utility class have three different static constants for creating empty List, Set and Map.

  • Collections.EMPTY_LIST
  • Collections.EMPTY_SET
  • Collections.EMPTY_MAP

There are also methods when you want to create type-safe empty collections.

  • Collections.emptyList()
  • Collections.emptySet()
  • Collections.emptyMap()

Bellow it the code example.

package org.kodejava.util;

import java.util.*;

public class EmptyCollectionDemo {
    public static void main(String[] args) {
        List list = Collections.EMPTY_LIST;
        System.out.println("list.size()  = " + list.size());
        Set set = Collections.EMPTY_SET;
        System.out.println("set.size()   = " + set.size());
        Map map = Collections.EMPTY_MAP;
        System.out.println("map.size()   = " + map.size());

        // For the type-safe example use the following methods.
        List<String> strings = Collections.emptyList();
        System.out.println("strings.size = " + strings.size());

        Set<Long> longs = Collections.emptySet();
        System.out.println("longs.size() = " + longs.size());

        Map<String, Date> dates = Collections.emptyMap();
        System.out.println("dates.size() = " + dates.size());
    }
}

The output are:

list.size()  = 0
set.size()   = 0
map.size()   = 0
strings.size = 0
longs.size() = 0
dates.size() = 0