I am attempting to solve a problem where I create a method that counts the number of occurrences of capital and lowercase ("A" or "a") in a certain string. I have been working on this problem for a week now, and the main error that I am receiving is that "char cannot be dereferenced". Can anyone point me in the correct direction on this Java problem? Thank you.
class Main{
public static int countA (String s)
{
String s1 = "a";
String s2 = "A";
int count = 0;
for (int i = 0; i < s.length; i++){
String s3 = s.charAt(i);
if (s3.equals(s1) || s3.equals(s2)){
count += 1;
}
else{
System.out.print("");
}
}
}
//test case below (dont change):
public static void main(String[] args){
System.out.println(countA("aaA")); //3
System.out.println(countA("aaBBdf8k3AAadnklA")); //6
}
}
try a simpler solution
String in = "aaBBdf8k3AAadnklA";
String out = in.replace ("A", "").replace ("a", "");
int lenDiff = in.length () - out.length ();
Also as #chris mentions in his answer, the String could be converted to lowercase first and then only do a single check
the main error that I am receiving is that "char cannot be
dereferenced"
change this:
s.length // this syntax is incorrect
to this:
s.length() // this is how you invoke the length method on a string
also, change this:
String s3 = s.charAt(i); // you cannot assign a char type to string type
to this:
String s3 = Character.toString(s.charAt(i)); // convert the char to string
another solution to accomplishing your task in a simpler manner is by using the Stream#filter method. Then convert each String within the Stream to lowercase prior to comparison, if any Strings match "a" we keep it, if not we ignore it and at the end, we simply return the count.
public static int countA(String input)
{
return (int)Arrays.stream(input.split("")).filter(s -> s.toLowerCase().equals("a")).count();
}
For counting the number of time 'a' or 'A' appears in a String:
public int numberOfA(String s) {
s = s.toLowerCase();
int sum = 0;
for(int i = 0; i < s.length(); i++){
if(s.charAt(i) == 'a')
sum++;
}
return sum;
}
Or just replace everything else and see how long your string is:
int numberOfA = string.replaceAll("[^aA]", "").length();
To find the number of times character a and A appear in string.
int numA = string.replaceAll("[^aA]","").length();
Related
I have successfully printed my String backwards, but I'm having a hard time getting it to shift forward a letter. My outputs have been numbers instead of letters, so I have tried to convert those numbers back to letters unsuccessfully. There is other code in this as well, but I only need help with this one bit.
package inlämningsuppgift4;
import java.util.Scanner;
public class Inlämningsuppgift4 {
public static void word(String w1){
//char a[]= w1.toCharArray();
for (int i=w1.length()-1; i>=0; i--)
//char c = 'a';
//c = (char) (((c - 'a' - 1) % 26) + 'a');
{System.out.print(w1.charAt(i));
}
System.out.println();
}
public static void word2(String w2){
for (int j=0;j<w2.length(); j++)
{System.out.print("*"+w2.charAt(j));
}
System.out.println("*");
}
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Ange ett ord: ");
String ord = input.nextLine();
word2(ord);
word(ord);
}
}
It seems like I was on the right path trying to set up "//char c" but I couldn't get it to function as written. I got that code from a questions search, but can't wrap my head around it. How do I make it fit with my code already written? Or should I find a different way?
You have two different problems:
reversing a string. There are a lot of ways to do it.
String s1 = "cat";
String s2 = "";
for (int i =0 ; i < s1.length(); i++) {
s2 = s1.charAt(i) + s2;
}
System.out.println(s2);
So just create a new string by adding strings backwards.
"Shifting" a character, which presumably means taking the code-point and modifying it, and possibly wrapping it (eg: Z wraps to A, instead of moving forward to [)
String s1 = "cat";
String s2 = "";
for (int i =0 ; i < s1.length(); i++) {
char c = s1.charAt(i);
c += 1;
// reverse string implementation omitted
}
System.out.println(s2);
Java seems to let you add directly to char so whatever works. Note that this does not care about wrapping, so z would not wrap to a. That's up to you to figure out.
Now you just need to combine that with the string building.
I'm tying to learn Java. I need to make a method called reverse that gets a string and return a string (but in reverse order). Here is what i tried. Can you fix the code and explain what I'm doing wrong? Please also give me some advice about a good start in Java. Thank you!
public class Test{
public static String reverse(String a){
int j = a.length();
char[] newWord = new char[j];
for(int i=0;i<a.length();i++)
{
newWord[j] = a.charAt(i);
j--;
}
return new String(newWord);
}
public static void main(String a[]){
String word = "abcdefgh";
System.out.println(reverse(word));
}
}
You can use this to reverse the string, you don't need to use your own method
new StringBuilder(word).reverse().toString()
If you want to use your solution you must change int j = a.length() to int j = a.length() -1;
The fixed code is
public class Test {
public static String reverse(String a) {
int j = a.length();
char[] newWord = new char[j];
for (int i = 0; i < a.length(); i++) {
newWord[--j] = a.charAt(i);
}
return new String(newWord);
}
public static void main(String a[]) {
String word = "abcdefgh";
System.out.println(reverse(word));
}
}
Like others have mentioned, arrays indexes start at 0. So if an array has size 5 for example it has indices 0,1,2,3,4. It does not have an index 5.
For an example of a string with length 5, the code change that I did newWord[--j] = a.charAt(i); will assign to the indices 4,3,2,1,0 in that order.
Regarding getting a good start in Java, I think you could try https://softwareengineering.stackexchange.com/. This site is not meant for that kind of thing.
This is a common difficulty with new Java developers.
The point you are missing is that the last entry in an array is at position a.length-1. Similarly for Strings
Here's an improved version to demonstrate.
public static String reverse(String a) {
char[] newWord = new char[a.length()];
for (int i = 0, j = a.length() - 1; i < a.length(); i++, j--) {
newWord[j] = a.charAt(i);
}
return new String(newWord);
}
You're already on the right track with your method. The one thing I will say to you is that you don't need to use an array of characters and then use something like return new String(newWord);. That's overly complicated for beginner Java in my view.
Instead, you can create an empty String and just keep appending the characters onto it as you loop through all the characters in the String you want to reverse.
So your for loop, because you're reversing the word, should begin at the end of the word being reversed (a in this case) and work backwards to index position 0 (ie. the start of the word being reversed).
Try this and see if this makes sense to you:
public static String reverse(String a) {
String reversedWord = "";
for (int index = a.length() - 1; index >= 0; index --) {
reversedWord += a.charAt(index);
}
return reversedWord;
}
This is, then, starting at the end of a, working backwards one character at a time (hence the use of index --) until we reach a point where index has gone beyond the character at index position 0 (the middle condition of index >= 0).
At each index position, we are simply taking the character from the a String and appending it onto the reversedWord String.
Hope this helps! Feel free to ask any other questions if you are stuck on this.
In your for loop, body must be as that
newWord[--j] = a.charAt(i);. It's because if the lenght of array is 8, its indexes are 0-7. So we first decrement j and then use it as array pointer.
public class Test {
public static String reverse(String a) {
int size= a.length();//size of string
char[] newWord = new char[size];//intialize
for (int i = size-1,j=0; i >=0 ; i--,j++) {//loop start from 7 to 0
newWord[j] = a.charAt(i);// and reverse string goes from 0 to 7
}
return new String(newWord);
}
public static void main(String a[]) {
String word = "abcdefgh";
System.out.println(reverse(word));
}
}
static void reverse {
String word = "Hello World";
StringBuilder str = new StringBuilder(word);
str.reverse();
System.out.println(str);
}
or you could do
new StringBuilder(word).reverse().toString()
public static void main(String[] args) {
String input = "hello world";
String output = new String();
for (int i = input.length() - 1; i >= 0; i--) {
output = output + input.charAt(i);
}
System.out.println(output);
}
package Reverse;
import java.util.*;
public class StringReverse {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter a String: ");
String original = input.nextLine();
String rev = "";// Initialize as Empty String
for(int i = original.length() - 1 ; i>=0 ; i--){
rev += original.charAt(i);
}
System.out.println("Reverse form: "+rev);
}
}
So i have been trying to make a code that counts the number of words in a string which was pretty easy. I'm running into problems when im trying to make it count the number of unique characters in a string. The program compiles and runs it doesn't display the number of Unique characters. Adding a System.out.println(countOfUniqueChars); below return doesn't work.
Here's the code:
public class Uniquechar{
public static void main(String[] args) {
String s = "Jag vet inte vad jag heter idag";
String[] parts = s.split(" ");
int wordcount = parts.length;
System.out.println("The number of words is" + wordcount);
countUniqueCharacters(s);
}
public static int countUniqueCharacters(String s) {
String lowerCase = s.toLowerCase();
char characters[] = lowerCase.toCharArray();
int countOfUniqueChars = s.length();
for (int i = 0; i < characters.length; i++) {
if (i != lowerCase.indexOf(characters[i])) {
countOfUniqueChars--;
}
}
return countOfUniqueChars;
}
Try this:
s = s.replace(" ", ""); // If you don't want to count space
char[] chars = s.toCharArray();
Set<Character> uniqueChars = new HashSet<>();
for (char c : chars) {
uniqueChars.add(c);
}
System.out.println(c.size());
Just print the method call, it prints the result.
System.out.println(countUniqueCharacters(s));
Adding a System.out.println(countOfUniqueChars); below return doesn't work.
It won't work. Because the code after return statement is unreachable. Perhaps you can do it just before return.
System.out.println(countOfUniqueChars);
return countOfUniqueChars;
You can do System.out.println(countUniqueCharacters(s)); in the main method, to output the return value of your method. After a return, you cannot add more code. I did it for you and the output is 12, so it seems to be that there is also something wrong with your algorithm.
int uniqeCharsCount = countUniqueCharacters(s);
System.out.println("The number of uniqe chars is " + uniqeCharsCount);
Output: 12
Your algorithm:
Actually you are checking every char, if this char is one more time in the string before. But you should also check if the char is anywhere in the string after the current index. You can fix it if you change your if condition to if (i != lowerCase.indexOf(characters[i]) || i != lowerCase.lastIndexOf(characters[i]))
Output of the fixed version: 3 (n, h, r)
I would recommend using a Set to retain only uniques, then count its size, instead of iterating:
public static int countUniqueCharacters(String s) {
String lowerCase = s.toLowerCase();
char characters[] = lowerCase.toCharArray();
Set<Character> uniques = new HashSet<Character>();
for (char c: characters) {
uniques.add(c);
}
return uniques.size();
}
if (i != lowerCase.indexOf(characters[i])) {
countOfUniqueChars--;
}
This is wrong. Your lowerCase string is lowercase, so any uppercase letters in characters[i] will have an index of -1 in lowerCase (will be calculated as a non-unique character). You can fix this by using indexOf(lowerCase.charAt(i));
A good way to count the number of characters would be eliminating repetitions. The ideia is get the first character, then find next occurrences and replace by nothing, once you do that you can count the unique characters.
public static int countUniqueCharacters(String s) {
String lowerCase = s.toLowerCase();
///Get the first char of lowerCase
String firstChar = lowerCase.substring(0,1);
//Take off the first char
String subS = lowerCase.substring(1);
///replace all chars equals to first char
String replacedSubS = subS.replace(firstChar, "");
/// Now, call method again to calculate size
/// of the substring with first char
// replaced by blank char
return 1+countUniqueCharacters(replacedSubS);
}
This method worked for me, take a look. You may do that in two lines, but i thought it's better be detailed here.
Adding a System.out.println(countOfUniqueChars); below return doesn't work.
That is expected behavior because return means that flow of control will be returned from method to place where this method was invoked. This means that code after return will not be executed, so in situation like
return countOfUniqueChars;
System.out.println(countOfUniqueChars);
System.out.println(countOfUniqueChars); would be dead code.
You could try printing value before you return it like
System.out.println(countOfUniqueChars);
return countOfUniqueChars;
or simply print returned value in main method like
int count = countUniqueCharacters(s);
System.out.println(count);
or using this one-liner
System.out.println(countUniqueCharacters(s));
BTW since Java 8 your code can look like
s.toLowerCase().chars().distinct().summaryStatistics().getCount()
or if you want to skip spaces you can add
s.toLowerCase().replace(" ","").chars().distinct().summaryStatistics().getCount()
public static int countUniqueCharacters(String s) {
char [] input=s.toCharArray();
Set<Character> charset=new HashSet<>();
for (int i = 0; i < input.length; i++) {
charset.add(input[i]);
}
return charset.size();
}
I am suppose to make a simple program that would take a users input, and put spaces between each single letter. So for example, user enters mall, and it returns M A L L(on same line).
I am trying to make a loop with a if statement in it.But I think I would need CharAt for it, so if the string is greater value then 1, I would declare a variable to everysingle character in the string(that the userinput). Then I would say put spaces between each letter. I am in AP computer science A, and we are practicing loops.Everything underthis, is what I have done so far. And the directions are in the comment above code.And im useing eclipse,java.
/**
* Splits the string str into individual characters: Small becomes S m a l l
*/
public static String split(String str) {
for (int i = 0; str.length() > i; i++) {
if (str.length() > 0) {
char space = str.charAt();
}
}
return str;
}
My solution uses concat to build the str2, and trim to remove last white space.
public static String split(String str) {
String str2 = "";
for(int i=0; i<str.length(); i++) {
str2 = str2.concat(str.charAt(i)+" ");
}
return str2.trim();
}
You don't modify method parameters, you make copies of them.
You don't null-check/empty-check inside the loop, you do it first thing in the method.
The standard in a for loop is i < size, not size > i... meh
/**
* Splits the string str into individual characters: Small becomes S m a l l
*/
public static String split(final String str)
{
String result = "";
// If parameter is null or empty, return an empty string
if (str == null || str.isEmpty())
return result;
// Go through the parameter's characters, and modify the result
for (int i = 0; i < str.length(); i++)
{
// The new result will be the previous result,
// plus the current character at position i,
// plus a white space.
result = result + str.charAt(i) + " ";
}
return result;
}
4. Go pro, use StringBuilder for the result, and static final constants for empty string and space character.
Peace!
Ask yourself a question, where is s coming from?
char space = s.charAt(); ??? s ???
A second question, character at?
public static String split(String str){
for(int i = 0; i < str.length(); i++) {
if (str.length() > 0) {
char space = str.charAt(i)
}
}
return str;
}
#Babanfaraj, this a answer from a newbie like you!!
The code is very easy. The corrected program is-
class fopl
{
public static void main(String str)
{
int n=str.length();
for (int i = 0;i<n; i++)
{
if (n>=0)
{
String space = str.charAt(i)+" ";
System.out.print(space);
}
}
}
}
Happy to help you!
I am working on a solution to the TSP problem. I have generated all the permutations of the String "123456", however, I need to convert this into an ArrayList of Integer like this [1,2,3,4,5,6]...[6,5,4,3,2,1]. I then store this into an ArrayList of ArrayLists. Once there I will be able to compare all of the cities that need to be traveled to.
When I run my code, I have a method to generate the permutation, then a method to change that permutation into an ArrayList of Integer. When I convert them, I get the exception java.lang.NumberFormatException: For input string: "". I don't know of any other way to get the String to Integer
Here is my code.
public static String permute(String begin, String string){
if(string.length() == 0){
stringToIntArray(begin+string);
return begin + string + " ";
}
else{
String result = "";
for(int i = 0; i < string.length(); ++i){
String newString = string.substring(0, i) + string.substring(i+1, string.length());;
result += permute(begin + string.charAt(i), newString);
}
stringToIntArray(result);
return result;
}
}
public static void stringToIntArray(String s){
ArrayList<Integer> perm = new ArrayList<Integer>();
String [] change = s.split("");
for(int i = 0; i < 7; ++i){
int integer = Integer.parseInt(change[i]);
System.out.println(integer);
}
}
public static void main(String[] args) {
permute("", "123456");
}
These lines
String [] change = s.split("");
for(int i = 0; i < 7; ++i){
int integer = Integer.parseInt(change[i]);
System.out.println(integer);
}
Given a String like "12345", when you split it on nothing, it will separate every character. Giving you an array with ["","1","2","3","4","5"]. Since the empty String "" is not a Number, you will get the NumberFormatException. You could change your index i to start at 1 so as to ignore that first empty String.
The split method, when splitting on "", produces an empty string as the first element of the array, so you need to start iterating from i = 1.
Also, it would be safer to stop the iteration at change.length to make sure you process all characters when there are more than 6, and don't go out of bounds if there are fewer.
String [] change = s.split("");
for(int i = 1; i < change.length; ++i){ // ignore first element
int integer = Integer.parseInt(change[i]);
System.out.println(integer);
}