I have written code to prompt user to input a sentence which will be displayed reversed by the system. I have managed it with a bit of help, but I now struggle to comment my codes to explain each piece of it. I somewhat understand what I have done, but I feel like I do not master the "whys" of each line.
Anyone able to help with my comments ?
public static void main(String[] args) {
// TODO Auto-generated method stub
String original = "", reverse = ""; // Setting the strings values
Scanner in = new Scanner(System.in); // Scanner is equal to input from user
while(!original.contains("exit"))
// As long as user does not input "exit", user will be prompt to enter a sentence
{
original = "";
reverse = "";
System.out.println("Enter a sentence to be reversed: ");
original = in.nextLine(); // Setting "original" to be equal to user's input
int length = original.length(); // Getting user's input character length (original)
for (int i = length - 1; i >= 0; i--) // Getting input from the last character to be reversed
reverse = reverse + original.charAt(i); //Setting "reverse" to the input "original" characters
System.out.println(reverse); // Printing the input reversely
}
}
Most blurry parts being the:
for (int i = length - 1; i >= 0; i--)
and the:
reverse = reverse + original.charAt(i);
Here's an explanation of what's happening.
public static void main(String[] args) {
String original = "", reverse = ""; // Create empty variables to hold the input and output
Scanner in = new Scanner(System.in); // Create an object to read from StdIn
while(!original.contains("exit"))
// Read from StdIn as long as user does not input "exit"
{
original = "";
reverse = "";
System.out.println("Enter a sentence to be reversed: ");
original = in.nextLine(); // Save the user's input as "original"
int length = original.length(); // Get the length of the input
for (int i = length - 1; i >= 0; i--) // Iterate over each character of the input, starting from the end until you reach the beginning and add the character to the "reverse" string
reverse = reverse + original.charAt(i);
System.out.println(reverse); // Output the result
}
}
Having two separate comments to explain the for loop doesn't make much sense as each of the two lines are meaningless without the other.
Well, let's look at it with the word 'HELLO' as input. You can tell, that the length of the string is 5, and the first letter (H) has the index 0, the second letter 1, ... and the last one has the index 4, which btw. is length -i.
The loop for (int i = length - 1; i >= 0; i--) starts with the last letter, then it takes the second last, and so on, and appends every letter in a reverse order to the reverse string. In general in the loop you will do following:
reverse = reverse + original.CharAt(4) => reverse='O'
reverse = reverse + original.CharAt(3) => reverse='OL'
reverse = reverse + original.CharAt(2) => reverse='OLL'
reverse = reverse + original.CharAt(1) => reverse='OLLE'
reverse = reverse + original.CharAt(0) => reverse='OLLEH'
Understanding
for (int i = length - 1; i >= 0; i--)
reverse = reverse + original.charAt(i);
Which you should reformat to look like
for (int i = length - 1; i >= 0; i--)
reverse = reverse + original.charAt(i);
or
for (int i = length - 1; i >= 0; i--) {
reverse = reverse + original.charAt(i);
}
means to take what is currently stored in the reverse variable and adding a new character at the end + original.charAt(i). This produces a new String which gets assigned back to the reverse variable, overriding what was in it before like #agim mentioned in his answer.
Here are some other alternatives you could consider. Especially with using StringBuilder because it has a reverse() function built into it, if you're wanting to reverse the sentence by character.
import java.util.*;
public class JavaFiddle
{
public static void main(String[] args)
{
String sentence = "The quick brown fox jumps over the lazy dog";
// Print sentence forward
System.out.println(sentence);
// Print sentence backwards by words
String[] words = sentence.split(" ");
for (int i = words.length - 1; i >= 0; i--) {
System.out.print(words[i] + " ");
}
System.out.println();
// Print sentence backwards by character
for (int i = sentence.length() - 1; i >= 0; i--) {
System.out.print(sentence.charAt(i));
}
System.out.println();
// Print sentence backwards by character using StringBuilder;
StringBuilder reverseSentence = new StringBuilder(sentence);
System.out.println(reverseSentence.reverse());
}
}
RESULT
The quick brown fox jumps over the lazy dog
dog lazy the over jumps fox brown quick The
god yzal eht revo spmuj xof nworb kciuq ehT
god yzal eht revo spmuj xof nworb kciuq ehT
Related
So i'm trying to count the number of upper-case characters in a array with strings. I'm at a brick wall here. If someone could shed some light on my problem that would be fantastic.
I assume the same loop can be done with just Character.isLowerCase(item) as well right?
After this is completed I also have to tell the user the longest string in the array and how many characters the longest string has as well which I really don't know how to do.
Professor really threw a curve ball at us with this one..
So here's my code so far:
// Program3.java
// Brandin Yoder
// 2/23/18
// Store strings in an array and tell user number of upper-case and lower-case characters,
// and spaces
import java.util.Scanner;
public class Program3
{
public static void main(String[] args)
{
// Set up keyboard.
Scanner keyboard = new Scanner(System.in);
// Input number of strings to store.
System.out.print("Number of strings to input: ");
int nrStrings = keyboard.nextInt();
// Clear keyboard buffer.
keyboard.nextLine();
// Set up array to hold strings.
String[] strings = new String[nrStrings];
// Input strings from keyboard.
System.out.println("\nInput strings:");
for(int ctr = 0; ctr < nrStrings; ctr++)
{
System.out.print("String #" + (ctr+1) + " :");
strings[ctr] = keyboard.next();
}
// Print back strings input.
System.out.println("\nStrings input:");
for(int ctr = 0; ctr < nrStrings; ctr++)
{
System.out.println("String #" + (ctr+1) + ": " + strings[ctr]);
}
// Set up variables for upper-case, lower-case and white space calculator.
int UpperNr = 0;
int LowerNr = 0;
int Spaces = 0;
// For loop that determines amount of Upper-Case numbers.
for(int ctr = 0; ctr < nrStrings; ctr++)
{
char item = strings[ctr].charAt(ctr);
if(Character.isUpperCase(item))
UpperNr++;
}
System.out.println(UpperNr);
}
}
You need to create variables to hold the data that you want to print out at the end. In this case you need to maintain an array that has the number of Uppercases for each string as well as the index and length of the longest string. You have to use a nested for loop to iterate through the array of strings that you have and also the strings themselves in order to check how many Uppercase characters you have. I have modified/commented the last part of your code below.
//array that contains number of uppercase letters in each string
int[] upperAmount = new int[nrStrings];
//index of the longest string
int maxLenIndex = 0;
//length of longest string
int maxLength = 0;
//array that iterates through all the strings in the array strings[]
for(int i = 0; i<strings.length;i++){
//if the new string is the longest
if(strings[i].length() > maxLength){
//set maxlength to the new length and record index of string
maxLength = strings[i].length();
maxLenIndex = i;
}
// For loop that determines amount of Upper-Case numbers.
for(int ctr = 0; ctr < strings[i].length(); ctr++)
{
char item = strings[i].charAt(ctr);
if(Character.isUpperCase(item))
UpperNr++;
}
//add number of uppercases to upperAmount array indexes will be the same
upperAmount[i] = UpperNr;
//reset upper number
UpperNr = 0;
}
// Print back strings input.
System.out.println("\nStrings input:");
for(int ctr = 0; ctr < nrStrings; ctr++)
{
System.out.println("String #" + (ctr+1) + ": " + strings[ctr]);
System.out.println("Number of Uppercase Letters: " + upperAmount[ctr]);
}
System.out.println("MaxStringLength: " + maxLength);
System.out.println("Max String: " + strings[maxLenIndex]);
}
I hope this solves your problem
//after you finish printing the strings
String strMax="";
int ctr=0;
for(String str :strings ){
strMax = str.length()>strMax.length()?str:strMax;
if(!str.equals(str.toLowerCase())){
for(char c : str.toCharArray()){
if(Character.isUpperCase(c))
ctr++;
}
}
}
System.out.println("Longeset String"+strMax );
System.out.println("total Upper case chars" +ctr);
Is it neccesarry to input the count of strings? I think you can accept one whole string and convert it into array of chars
char[] charArray = acceptedString.toCharArray;
Then go throw all chars, and where charArray[n] > 64 && charArray[n] < 91 increase your variable to counting UpperCases. Hope you understand) Ask if you have questions.
Scanner keyboard = new Scanner(System.in);
String inString = keyboard.nextLine();
char[] symbol = inString.toCharArray();
int count =0;
for(int i =0; i < symbol.length; i++){
if(symbol[i] > 64 && symbol[i] < 91){ //cause every char has its own number in Unicode. 'A' = 65 and 'Z' = 90
count++;
}
}
System.out.print(count);
I've searched about everywhere but I just can't find anything very concrete. I've been working on this code for awhile now but it keeps stumping me.
public static void main(String[] args) {
System.out.println(palindrome("word"));
}
public static boolean palindrome(String myPString) {
Scanner in = new Scanner(System.in);
System.out.println("Enter a word:");
String word = in.nextLine();
String reverse = "";
int startIndex = 0;
int str = word.length() -1;
while(str >= 0) {
reverse = reverse + word.charAt(i);
}
}
There's a lot of ways to accomplish this using a while loop.
Thinking about simplicity, you can imagine how could you do this if you had a set of plastic separated character in a table in front of you.
Probably you'll think about get the second character and move it to the begin, then get the third and move to begin, and so on until reach the last one, right?
0123 1023 2103 3210
WORD -> OWRD -> ROWD -> DROW
So, you'll just need two code:
init a variable i with 1 (the first moved character)
while the value of i is smaller than total string size do
replace the string with
char at i plus
substring from 0 to i plus
substring from i+1 to end
increment i
print the string
The process should be:
o + w + rd
r + ow + d
d + row +
drow
Hope it helps
Here is an piece of code I write a while back that uses almost the same process. Hope it helps!
String original;
String reverse = "";
System.out.print("Enter a string: ");
original = input.nextLine();
for(int x = original.length(); x > 0; x--)
{
reverse += original.charAt(x - 1);
}
System.out.println("The reversed string is " +reverse);
I'm trying to write my own Java word count program. I know there may already be a method for this, but I'd like to get it work. I'm getting an out of bounds error at line 14. I'm trying to use an input word to count how many times it appears in an input string. So I'm looping up to stringlength - wordlength, but that's where the problem is.
Here is the code:
import java.util.Scanner;
public class wordcount {
public static void main(String[] args)
{
Scanner s = new Scanner(System.in);
System.out.print( "Enter word : " );
String word = s.nextLine();
Scanner t = new Scanner(System.in);
System.out.print("Enter string: ");
String string = t.nextLine();
int count = 0;
for (int i = 0; i < string.length()-word.length(); i = i+1){
String substring = string.substring(i,i+word.length());
if (match(substring, word)==true){
count += 1;
}
}
System.out.println("There are "+count+ " repetitions of the word "+word);
}
public static boolean match(String string1, String string2){
for (int i=0; i<string1.length(); i+=1){
if (string1.charAt(i)!=string2.charAt(i)){
return false;
}
}
return true;
}
}
First of all, two Scanners are not necessary, you can do many inputs with the same Scanner object.
Also, this if condition
if (match(substring, word) == true)
can be rewritten like
if (math(substring, word))
I would also recommend you to use i++ to increase the loop variable. Is not strictly necessary but is "almost" a convention. You can read more about that here.
Now, about theIndexOutOfBoundsException, I've tested the code and I don't find any input samples to get it.
Besides, there is an issue, you are missing one iteration in the for:
for (int i = 0; i < string.length() - word.length() + 1; i++) { // Add '+ 1'
String substring = string.substring(i, i + word.length());
// System.out.println(substring);
if (match(substring, word)) {
count++;
}
}
You can test it by putting a print statement inside the loop, to print each substring.
I'm not getting an out of bounds error, can you tell me what values you were using for word and string?
I have identified a bug with your program. If word is equal to string, it still returns count 0. I suggest adding one more iteration and using regionMatches instead. RegionMatches makes your match method obsolete and will return false if word.length() + i is equal or greater than string.length(), avoiding out of bounds issues.
As you can see I also moved the calculations to a seperate method, this will make your code more readable and testable.
And as Christian pointed out; you indeed do only need one Scanner object. I've adapted the code below to reflect it.
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print("Enter word : ");
String word = sc.nextLine();
System.out.print("Enter string: ");
String string = sc.nextLine();
int count = calculateWordCount(word, string);
System.out.println("There are " + count + " repetitions of the word " + word);
}
private static int calculateWordCount(String word, String string) {
int count = 0;
for (int i = 0; i < string.length() - word.length() + 1; i++) {
if (word.regionMatches(0, string, i, word.length())) {
count++;
}
}
return count;
}
I am a student at the moment so I am still learning. I picked up VB pretty quick and it was simple Java on the other hand I am pretty confused on.
The Assignment I have been given this time has me confused "Write a method to determine the number of positions that two strings differ by. For Example,"Peace" and "Piece" differ in two positions. The method is declared int compare(String word1, String word2); if the strings are identical, the method returns 0. It returns -1 if the two strings have different lengths."
Additional "Write a main method to test the method. The main method should tell how many, positions the strings differ, or that they are identical, or if they are different lengths, state the lengths. Get the strings from the console.
So far this is where I am at and I am looking for someone to help break this down in I DUMDUM terms if they can I don't need a solution only help understanding it.
package arraysandstrings;
import java.util.Scanner;
public class differStrings {
public static void main (String agrs[]){
Scanner scanner = new Scanner (System.in);
System.out.print("Enter a word");
String word1;
String word2;
word1 = scanner.next();
System.out.print("Enter another word");
word2 = scanner.next();
int count = 0;
int length = word1.length();
for(int x = 0; x >= length; x = x+1) {
if (word1.charAt(x) == word2.charAt(x)) {
count = count + 1;
System.out.print (count);
}
}
}
}
Additional Question
package arraysandstrings;
import java.util.Scanner;
public class differStrings {
public static void main (String agrs[]){
Scanner scanner = new Scanner (System.in);
System.out.println("Enter a word");
String word1 = scanner.next();
System.out.println("Enter another word");
String word2 = scanner.next();
int count = 0;
int word1Length = word1.length();
int word2Length = word2.length();
if (word1Length != word2Length) {
System.out.println ("Words are a diffrent length");
System.out.println (word1 + "Has" + word1.length() + " chars");
System.out.println (word2 + "Has" + word2.length() + " chars");
}
for(int x = 0; x < word1Length; x = x+1) {
if (word1.charAt(x) != word2.charAt(x)) {
count = count + 1;
}}}
System.out.println (count+" different chars");
}
After implementing the knowledge Iv gained from your responses I have ran in to a problem with the last line:
System.out.println (count+" different chars");
It says Error expected however it worked before I added the next part of my assignment which was this:
if (word1Length != word2Length) {
System.out.println ("Words are a diffrent length");
System.out.println (word1 + "Has" + word1.length() + " chars");
System.out.println (word2 + "Has" + word2.length() + " chars");
}
for(int x = 0; x >= length; x = x+1) {
You probably mean
for(int x = 0; x < length; x = x+1) {
Shifting around some code, adding some line breaks and making 2 small tweaks to the logic produces a program that is closer to what you are trying to build.
package arraysandstrings;
import java.util.Scanner;
public class differStrings {
public static void main (String agrs[]){
Scanner scanner = new Scanner (System.in);
System.out.println("Enter a word");
String word1 = scanner.next();
System.out.println("Enter another word");
String word2 = scanner.next();
int count = 0;
int length = word1.length();
for(int x = 0; x < length; x = x+1) {
if (word1.charAt(x) != word2.charAt(x)) {
count = count + 1;
}
}
System.out.println (count+" different chars");
}
}
It looks like in addition to the for loop that #LouisWasserman pointed out you had code that was trying to find characters that are the same.
What you need is a loop which compares the two strings and counts the places where they are not equal.
Your logic counts the number of places where the two characters are the same. You are also printing the count each time the two characters are equal.
What it sounds like you need is a loop that iterates over the characters in the two strings comparing each character and incrementing the count of mis-matched or different characters. Then after getting a count of different characters by comparing all of the characters, you would print out the count of different characters.
So the basics would be: (1) read each of the strings, (2) check that the lengths are the same, (3) if same length then loop over the string comparing each character and incrementing the count of mis-matched characters each time there is a difference, (4) print out the count. If the string lengths are different then just set the count to negative one (-1) and do not bother to compare the two strings.
What would be kind of neat to do is to create a string of underscores and asterisk, in which each matching character position is represented by an underscore and each mis-matching character position is represented by an asterisk or perhaps the string would contain all of the matching characters and the mis-matching characters would be replaced by an asterisk.
Edit: adding example program
The example below is an annotated rewrite of your program. One change that I made was to use a function to perform the counting of the non-matching characters. The function, countNonMatchChars () is a static function in order to work around the object oriented nature of Java. This function is a utility type function and not really part of a class. It should be available to anyone who wants to use it.
Also rather than incrementing variables with the syntax of var = var + 1; I instead use the postincrement operator of ++ as in var++;.
package arraysandstrings;
import java.util.Scanner;
public class so_strings_main {
// function to compare two strings and count the number
// of characters that do not match.
//
// this function returns an integer indicating the number
// of characters that did not match or a negative one if the
// strings are not equal in length.
//
// "john" "john" returns 0
// "john1" "john2" returns 1
// "mary1" "john1" returns 4
// "john" "john1" returns -1 (lengths are not equal)
public static int countNonMatchChars (String s1, String s2)
{
// initialize the count to negative one indicating strings unequal in length
// get the lengths of the two strings to see if any comparison is needed
int count = -1;
int word1Length = s1.length();
int word2Length = s2.length();
if (word1Length == word2Length) {
// the lengths of the two strings are equal so we now do our comparison
// we start count off at zero. as we find unmatched characters, we
// will increment our count. if no unmatched characters found then
// we will return a count of zero.
count = 0;
for(int iLoop = 0; iLoop < word1Length; iLoop++) {
if (s1.charAt(iLoop) != s2.charAt(iLoop)) {
// the characters at this position in the string do not match
// increment our count of non-matching characters
count++;
}
}
}
// return the count of non-matching characters we have found.
return count;
}
public static void main (String agrs[]){
Scanner scanner = new Scanner (System.in);
System.out.println("Count non-matching characters in two strings.");
System.out.println("Enter first word");
String word1 = scanner.next();
System.out.println("Enter second word");
String word2 = scanner.next();
int count = countNonMatchChars (word1, word2);
if (count < 0) {
System.out.println ("Words are a diffrent length");
System.out.println (" " + word1 + " Has " + word1.length() + " chars");
System.out.println (" " + word2 + " Has " + word2.length() + " chars");
} else {
System.out.println (count + " different chars");
}
}
}
this was the solution to my homework and the purpose was to reverse each word in a string based on user inputting a sentence. I have completed this on my own, but I'm just wondering how the iterator worked in this piece of code. I don't understand the delcaration of tempword = ""; and how he printed out each word delimited by spaces.
import java.util.Scanner;
public class StringReverser
{
public static void main(String args[])
{
String sentence;
String word;
String tempWord = "";
Scanner scan = new Scanner(System.in);
Scanner wordScan;
System.out.print("Enter a sentence: ");
sentence = scan.nextLine();
wordScan = new Scanner(sentence);
while(wordScan.hasNext())
{
word = wordScan.next();
for(int numLetters = word.length() - 1; numLetters >= 0; numLetters--)
tempWord += word.charAt(numLetters);
System.out.print(tempWord + " ");
tempWord = "";
}
System.out.println();
}
}
this bit adds in the spaces
System.out.print(tempWord + " ");
this bit reverses it
for(int numLetters = word.length() - 1; numLetters >= 0; numLetters--)
tempWord += word.charAt(numLetters);
this bit sets it up for the next word
tempWord = "";
The for loop counts backwards, from the index of the last character in the word to the first (in zero based notation)
The print prints the reversed word + a space (" "), the fact it uses print in place of println is because println would add a carriage return putting each word in a different line.
The tempWord = ""; at the end of each iteration reset the variable so it can be reused.