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