How do I know if a character is lowercase?

By Wayan in Core API, Lang Package 0 Comment

In this example you are going to learn another example on using the java.lang.Character class. The Character.isLowerCase() method can be used to determine if a letter is a lowercase letter. This method takes a char as argument and return a boolean value. If it returns true it means the character is in lowercase form. And if it returns false it means the character is not in lowercase form.

Beside using the isLowerCase() method you can also compare the character type with the constant value of Character.LOWERCASE_LETTER. To get the character type you can use the Character.getType() method. You can see the example on the following code snippet.

package org.kodejava.lang;

public class CharacterIsLowerCaseExample {
    public static void main(String[] args) {
        char a = 'a';

        // Checks to see if a letter is a lowercase letter.
        if (Character.isLowerCase(a)) {
            System.out.println(a + " is a lowercase letter.");
        }

        // Checks to see if a letter is a lowercase letter
        // by comparing the character type against
        // Character.LOWERCASE_LETTER constant value.
        int charType = Character.getType(a);
        if (charType == Character.LOWERCASE_LETTER) {
            System.out.println(a + " is a lowercase letter.");
        }
    }
}

This example give you the following output:

a is a lowercase letter.
a is a lowercase letter.

How do I check if a character representing an alphabet?

By Wayan in Core API, Lang Package 2 Comments

In the previous example you’ve learned how to use the Character.isDigit() method to check if a character representing a digit.

In this example you will learn how to check if a character representing a letter. You can use the Character.isLetter(char c) method to check if a character is a valid letter. This method will return a true value for a valid letter characters and false if the character is not a valid letter.

In the code snippet below you will also learn how to use the toCharArray() method to covert a string into an array of char. Here we use the method so that we can check every character in the for-each loop to see is the character is a letter or not.

package org.kodejava.lang;

public class CharacterIsLetterExample {
    public static void main(String[] args) {
        String name = "Kode Java 123";

        // Determines if the specified character is a letter
        if (Character.isLetter(name.charAt(5))) {
            System.out.println("The fifth character (" +
                    name.charAt(5) + ") is an alphabet!");
        }

        // Iterates all characters in the string to see if it is
        // a letter or not.
        for (char c : name.toCharArray()) {
            if (Character.isLetter(c)) {
                System.out.println(c + " is a letter.");
            } else {
                System.out.println(c + " not a letter.");
            }
        }
    }
}

The code will print the following output:

The fifth character (J) is an alphabet!
K is a letter.
o is a letter.
d is a letter.
e is a letter.
  not a letter.
J is a letter.
a is a letter.
v is a letter.
a is a letter.
  not a letter.
1 not a letter.
2 not a letter.
3 not a letter.

How do I check if a character representing a number?

By Wayan in Core API, Lang Package 0 Comment

For validation purposes we might need to check if data entered by our users is a valid data for our application to process. A simple mechanism for checking if a character inputted is a digit or not can be done by using the java.lang.Character class isDigit(char c) method.

In this example you will learn how to check if a character representing a number. You will start by creating a string that contains some random alphanumeric characters in it. And then you are going to iterate these characters, get the value at the specific location using the charAt() method. In the last section you are going to check to if the character represent a digit or not.

package org.kodejava.lang;

public class CharacterIsDigitExample {
    public static void main(String[] args) {
        // Manually creates a string with randoms characters.
        String str = "12?XYZ4!6cba78+HI@0";

        for (int i = 0; i < str.length(); i++) {
            // Determines if the specified character is a digit
            if (Character.isDigit(str.charAt(i))) {
                System.out.println(str.charAt(i) + " is a digit.");
            } else {
                System.out.println(str.charAt(i) + " not a digit.");
            }
        }
    }
}

These are the outputs of our program:

1 is a digit.
2 is a digit.
? not a digit.
X not a digit.
Y not a digit.
Z not a digit.
4 is a digit.
! not a digit.
6 is a digit.
c not a digit.
b not a digit.
a not a digit.
7 is a digit.
8 is a digit.
+ not a digit.
H not a digit.
I not a digit.
@ not a digit.
0 is a digit.

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How do I know if an ArrayList contains a specified item?

By Wayan in Core API, Util Package 2 Comments

In this example we are going to learn how to find out if an ArrayList object contains the specified element. To check if an ArrayList object contains the specified element we can use the contains(Object o) method. This method returns a boolean true when the specified element is found in the ArrayList, otherwise return false. The method returns true if and only if the list contains at least one element, where the element equals to the item in the list.

Let’s see the code snippet below to demonstrate it.

package org.kodejava.util;

import java.util.ArrayList;
import java.util.List;

public class ArrayListContainsExample {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("Item 1");
        list.add("Item 2");
        list.add("Item 3");
        list.add("Item 4");

        // Check to see if the list contains "Item 1".
        String itemToFind = "Item 1";
        System.out.println("contains(" + itemToFind + "): " + list.contains(itemToFind));

        // Check to see if the list contains "Item 20".
        itemToFind = "Item 20";
        System.out.println("contains(" + itemToFind + "): " + list.contains(itemToFind));
    }
}

The output of the code snippet above are:

contains(Item 1): true
contains(Item 20): false

How do I know the size of ArrayList?

By Wayan in Core API, Util Package 0 Comment

In this example we are going to learn how to obtain the size of an ArrayList object. As you might already know, a java.util.ArrayList is a class that we can use to create a dynamic sized array. We can add and remove elements from the ArrayList dynamically.

Because its elements can be added or removed at anytime, we might want to know the number of elements currently stored in this list. To obtain the size we can use the size() method. This method returns an int value that tells us the number of elements stored in the ArrayList object.

When the list contains more than Integer.MAX_VALUE elements this method returns Integer.MAX_VALUE.

package org.kodejava.util;

import java.util.ArrayList;
import java.util.List;

public class ArrayListSize {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("Item 1");
        list.add("Item 2");
        list.add("Item 3");

        int size = list.size();
        System.out.println("List size = " + size);
    }
}

In the code snippet above we start creating an instance of ArrayList that can holds String values. As a good practice we should always use the interface as the type of the declared object, in this case we use the List interface. The <> is a diamond operator, started from JDK 7 you can use this operator so that you don’t need to repeat the generic type twice between the declaration and instantiation.

After we create the ArrayList object and add string elements to the list object, we get the size of the list by calling the size() method. We store the result in the size variable and print out its value. If you compile and run the code above you will get the following output:

List size = 3