Develop Reference

Count Vowels and Consonants

I was exploring this code which gives a count of vowels and consonants, but didn't understand this else if (ch >= 'a' && ch <= 'z') line of code. Please tell me what's the logic behind it.
import java.util.Scanner;
public class Vowels {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc = new Scanner(System.in);
System.out.println("Enter string");
String str = sc.nextLine();
int vowl = 0;
int conso = 0;
for (int i = 0; i < str.length(); i++) {
char ch = str.charAt(i);
if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
vowl++;
} else if (ch >= 'a' && ch <= 'z') {
conso++;
}
}
System.out.println(vowl);
System.out.println(conso);
}
}

A benefit of chars is that you can operate with them like if they were integers.
For example, you can do you this as well 'a' + 3 = 'd'
Meaning that 'a' < 'd' = true.

notice the if statement catches all vowels
whats ever is not a vowel will either be a capital letter, a number, a special character or consonants
else if (ch >= 'a' && ch <= 'z')
this checks if its not a vowel does it atleast fall in the range of small letter 'a'-'z' and is not a special charecter or a number.( we knonw its not a vowel but is it in the ascii range 26=a -51=z)
refer to the ASCII table to understand the range comparison

The comparison of characters the way it is done can create confusion, as you can see from Java: Character comparison.
Basically #TDG is correct by saying that ch is checked to be between 'a' and 'z', and thus the check might be translated as "is ch a lower case character?"
The tricky part is that depending on the language people use the expectation can be different, especially since language specific characters are not taken into account. In German language, 'ö' would definitely qualify as lower case character but is not in the range of the check. The complexity may get evident by studying the Unicode code charts.
The best check is to use Character.isLowerCase().

char is a character that represented by a number which is the index of the character in the ASCII/unicode table, since the the alphabet characters are arranged in order in the ASCII table, the following code checks if the ch is in the range of the lowercase alphabet characters representation which is 97 to 122 in the table.
using (int) ch you can see the decimal value of the character and can compare it with the index in the ASCII table.
you can see the ASCII table here:https://www.asciitable.com/

How to prevent IntelliJ to stop continuing double-slash comments on the next line?

Short version
When pressing <enter> at the end of a // comment, Intellij sometimes decides to continue the // comment on the next line. How can I prevent that? Is there a setting somewhere to disable this automation?
Long version
There is a thing I do regularily, it is to break a long expression with a double-slash.
Let's say I have a line like
boolean isHex = c >= '0' && c <= '9' || c >= 'A' && c <= 'F' || c >= 'a' && c <= 'f';
and I want to split it like that
boolean isHex = c >= '0' && c <= '9' //
|| c >= 'A' && c <= 'F' //
|| c >= 'a' && c <= 'f';
Note that I want the final // in order to prevent any formatter to join the lines again.
So I insert a double-slash-return after the '9', by pressing //<enter>. But Intellij will auto-continue the comment on the next line.
boolean isHex = c >= '0' && c <= '9' //
// || c >= 'A' && c <= 'F' || c >= 'a' && c <= 'f';
It forces me to uncomment and reindent the line manually.
I want Intellij to not continue the comment on the next line and optionally indent my code:
boolean isHex = c >= '0' && c <= '9' //
|| c >= 'A' && c <= 'F' || c >= 'a' && c <= 'f';
So I want to disable this "continue // comment after <enter>" feature. Is it possible? I haven't found any setting related to that.

The closest you are going to get is to define a macro to insert a new line and remove the comment and then bind that macro to a suitable key.

Go to Settings → Code Style → Java → Wrapping and Braces and check "Line breaks" under "Keep when reformatting". This will make IntelliJ's formatter respect any manual line breaks, even if they contradict other formatting rules.

Confused About Integer and Char Type

There is a code like this :
boolean isValid(int ch) {
if(ch < '1' | ch > '7' & ch != 'q') return false;
else return true;
}
class HelpClassDemo {
...
do {
choice=(char) System.in.read();
} while(!hlpobj.isValid(choice));
}
That's the question :
Why we used int ch in isValid(int ch) in spite of choice's type is char?
Shouldn't we use char ch ? If we should use int ch why there is a code like this : (ch < '1' | ch > '7' & ch != 'q')
Isn't ch<1 or ch>7 logical ? I know it's a quite simple question but I'm confused about this.

A int type as a wider range than a char type (see this data type range table). IMO, receiving a char as an int provides you with some kind of overflow protection (points of view on this are welcome) but it is not something I'd do as I'd use the right data type instead.
Now, when you compare
if(ch < '1' | ch > '7' & ch != 'q') return false;
you are implicitly casting '1' and '7' to int type, which is perfectly valid.
And finally, regarding
Isn't ch<1 or ch>7 logical ? I know it's a quite simple question but
I'm confused about this.
It is logical, but it's not the same.
If you do ch > '1' && ch < '7', you are comparing ch to the ASCII value of 7, which is 55, and value of 1, which is 48. Basically, you are making sure that ch is a char between 2 and 6, both inclusive.
But if you do ch > 1 && ch < 7, you are comparing integers and validating that the char represented by ch is between 2 and 6 (both inclusive). This char is very likely to be not-human-readable.
If you want to make them equivalent, you wold have to compare according to the appropiate char value, like
if (ch > 48 && ch < 55)

To check whether a character is of English Alphabet (a-zA-Z)

The method Character.isLetter(Char c) tells whether the character is a unicode letter. What if I want to check for English letters (a-zA-Z) without regex.

Easy
char c = ...;
if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')) {
//english letter
}

Cannot get program to recognize capital letters when input?

Java beginner here - hoping someone can help me solve this problem. I am trying to write a simple program that will display a particular message depending on the character entered by the user. The problem I'm having is that it won't recognize the validity of capitalized characters in determining which message to print.
The code compiles OK but if I enter a capital letter, it prints out the message telling me it is not a valid character to start an identifier.
Here is a snippet of the source code:
choice2 = (char) System.in.read();
if(choice2 == 'q')
break;
else
if(choice2 == '_' || choice2 >= 'a' && choice2 <= 'z' && choice2 >= 'A' && choice2 <= 'Z' && choice2 > '0' && choice2 <= '9')
System.out.println("That is a valid character to start an identifier.");
else
if(choice2 == '$')
System.out.println("That is a valid character to start an identifier but should only be used by mechanically generated source code");
else
System.out.println("Sorry, that is not a valid character to start an identifier");
break;
Is there something I'm doing wrong or is it something inherent to the char data type?
Thanks

The problem is with your boolean groupings and a couple && should be ||
if (choice2 == '_' ||
((choice2 >= 'a' && choice2 <= 'z') ||
(choice2 >= 'A' && choice2 <= 'Z') ||
(choice2 > '0' && choice2 <= '9')))
This will evaluate to true if choice2 == '_' OR if choice2 is either between a and z inclusive, between A and Z inclusive, or between 0 and 9 inclusive.