How do I use StringTokenizer to split a string?

By Wayan in Core API, Util Package 0 Comment

The code below is an example of using StringTokenizer to split a string. In the current JDK this class is discouraged to be used, use the String.split(...) method instead or using the new java.util.regex package.

package org.kodejava.util;

import java.util.StringTokenizer;

public class StringTokenizerExample {
    public static void main(String[] args) {
        StringTokenizer st =
            new StringTokenizer("A StringTokenizer sample");

        // get how many tokens inside st object
        System.out.println("Tokens count: " + st.countTokens());

        // iterate st object to get more tokens from it
        while (st.hasMoreElements()) {
            String token = st.nextElement().toString();
            System.out.println("Token = " + token);
        }

        // split a date string using a forward slash as delimiter
        st = new StringTokenizer("2021/09/14", "/");
        while (st.hasMoreElements()) {
            String token = st.nextToken();
            System.out.println("Token = " + token);
        }
    }
}

Here is the result of this sample code:

Tokens count: 3
Token = A
Token = StringTokenizer
Token = sample
Token = 2021
Token = 09
Token = 14

How do I check a string starts with a specific word?

By Wayan in Core API, Lang Package 0 Comment

To test if a string starts with a specific prefix we can use the String.startsWith(String prefix) method. This method returns a boolean true as the result if the string starts with that specified prefix. The String.startsWith() method checks the prefix in case-sensitive manner.

The following code snippet give us a small example how to use this method, but instead of just straightly checks using the startsWith() method, we add a scanner that allows us to input the prefix that we want to test.

package org.kodejava.lang;

import java.util.Scanner;

import static java.lang.System.in;

public class StringStartsWithExample {
    private static final Scanner scanner = new Scanner(in);

    public static void main(String[] args) {
        String text = "The quick brown fox jumps over the lazy dog";
        System.out.println("Text: " + text);

        System.out.print("Type the prefix to test: ");
        String search = scanner.nextLine();

        // Check if the text start with the search text.
        if (text.startsWith(search)) {
            System.out.println("Yes, the fox is the quick one");
        } else {
            System.out.println("The fox is a slow fox");
        }
    }
}

The code snippet print the following output:

Text: The quick brown fox jumps over the lazy dog
Type the prefix to test: The quick brown fox
Yes, the fox is the quick one

How do I check a string ends with a specific word?

By Wayan in Core API, Lang Package 0 Comment

The String.endsWith() method can be used to check if a string ends with a specific word. It will return a boolean true if the suffix is found at the end of the string object.

In this example we will start the code by creating a class called StringEndsWithExample. This class has a standard main() method that makes the class executable. In the main() method we create a string variable called str and assign a text to it.

On the following line you can see an if conditional statement to check it the str string ends with "lazy dog". If it ends with that words then the corresponding block in the if statement will be executed.

package org.kodejava.lang;

public class StringEndsWithExample {
    public static void main(String[] args) {
        String str = "The quick brown fox jumps over the lazy dog";

        // well, does the fox jumps over a lazy dog?
        if (str.endsWith("lazy dog")) {
            System.out.println("The dog is a lazy dog");
        } else {
            System.out.println("Good dog!");
        }

        // Ends with empty string.
        if (str.endsWith("")) {
            System.out.println("true");
        }

        // Ends with the same string.
        if (str.endsWith(str)) {
            System.out.println("true");
        }
    }
}

Another thing that you need to know is that the endsWith() method will return true if you pass in an empty string or another string that is equals to this string as the argument. This method is also case-sensitive.

When you run the code snippet above you can see the following lines printed out:

The dog is a lazy dog
true
true

How do I know the length of a string?

By Wayan in Core API, Lang Package 0 Comment

To get the length of a String object we can use the String.length() method. This method returns the string length as an int value. The length of the string is equals to the length of the sequence of characters represented by this string object, and it is equals to the number of 16-bit Unicode characters in the string.

The following code snippet shows how to use the length() method. We create a string object name and assign a text to it. Call the method and store the length returned to the length variable and print it out. We can also use the length() method to check if the string is empty by checking if the length is equals to zero.

package org.kodejava.lang;

public class StringLengthExample {
    public static void main(String[] args) {
        String name = "Kode Java - Learn Java by Examples";

        // Get the length of the string specified by the name
        // variable.
        int length = name.length();
        System.out.println("Length = " + length);

        // Set name to an empty string and test if it is empty.
        name = "";
        length = name.length();
        if (length == 0) {
            System.out.println("The string is empty!");
        }
    }
}

If you run this code you will get the following output:

Length = 34
The string is empty!

How do I check string for equality?

By Wayan in Core API, Lang Package 0 Comment

To compare strings for their content equality we must use the String.equals() method. This method ensures that it will compare the content of both string instead of the object reference of the both string. This method returns true if both string in comparison have the same content.

Do not, never, use the == operator to compare string for its content. The == operator check for object reference equality, it returns true only if both objects point to the same reference. This operator returns false if the object doesn’t point to the same references.

package org.kodejava.lang;

public class StringEquals {
    public static void main(String[] args) {
        String s1 = "Hello World";
        String s2 = new String("Hello World");

        // This is good!
        if (s1.equals(s2)) {
            System.out.println("1. Both strings are equals.");
        } else {
            System.out.println("1. Both strings are not equals.");
        }

        // This is bad!
        if (s1 == s2) {
            System.out.println("2. Both strings are equals.");
        } else {
            System.out.println("2. Both strings are not equals.");
        }
    }
}

In the example above we deliberately create an instance of s2 string using the new operator to make sure that we have a different object reference. When you run the program it will give you the following result:

1. Both strings are equals.
2. Both strings are not equals.

How do I check if a string contains a specific word?

By Wayan in Core API, Lang Package 1 Comment

In this code example we are going to learn how to find a specific word or text inside a string. For this example we will utilize the java.lang.String class. The String class provides a method called String.indexOf(). It takes an argument of a String, which is the sub string that we want to find in the other string. You can imagine the sub string as a needle that we are going to find in the haystack.

If the word found more than once in the string, the indexOf() method returns the first index of a sub string found in the specified string. If the sub string can’t be found this method returns -1. The index of string returns by this method begin at zero. It means that the first letter in the string have the index number 0.

Another way that we can use is the String.contains() method. This method introduced in JDK 1.5. The method simply return a boolean value which is true or false indicating whether the string in search is found in the haystack. Let’s see the snippet below:

package org.kodejava.lang;

public class StringContainsExample {
    public static void main(String[] args) {
        String haystack = "Kodejava - Learn Java by Examples";

        // Checks to see if the word "Java" is found in the haystack
        // variable.
        String needle = "Java";
        if (haystack.indexOf(needle) != -1) {
            System.out.println("Found the word " + needle +
                    " at index number " + haystack.indexOf(needle));
        } else {
            System.out.println("Can't find " + needle);
        }

        // Or use the String.contains() method if you are not interested
        // with the index of the word.
        if (haystack.contains(needle)) {
            System.out.println("Eureka we've found Java!");
        }
    }
}

Running the example gave you the following result:

Found the word Java at index number 17
Eureka we've found Java!

How do I know if a character is uppercase?

By Wayan in Core API, Lang Package 0 Comment

In the previous example How do I know if a character is lowercase?, we’ve learned how to use the Character.isLowerCase() method. Now we will learn how to use the other method, which is the Character.isUpperCase() to determine if a letter is in an uppercase form. This method also return a boolean value that indicates whether the character is in uppercase form or not.

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Another way to check if a letter is in uppercase form is by comparing the type of the characters, that can be obtained using the Character.getType() method with a defined constant value Character.UPPERCASE_LETTER.

Below is the code snippet that demonstrate these methods.

package org.kodejava.example.lang;

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

        // Checks to see if a letter is a uppercase letter.
        if (Character.isUpperCase(a)) {
            System.out.println(a + " is an uppercase character.");
        }

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

The above example give you the following result when it executed:

A is an uppercase character.
A is an uppercase character.

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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