Develop Reference

Reversing strings in Java (loops) until "done"

this is a lab for class I'm trying to do. Here's the instructions:
Write a program that takes in a line of text as input, and outputs that line of text in reverse. The program repeats, ending when the user enters "Done", "done", or "d" for the line of text.
Ex: If the input is:
"Hello there
Hey
done"
the output is:
"ereht olleH
yeH"
And here's what I have right now:
public class LabProgram {
public static void main(String[] args) {
/* Type your code here. */
Scanner scnr = new Scanner(System.in);
String[] inputs = new String[100];
String input;
int i = 0;
while (true) {
input = scnr.nextLine();
if(input.equals("Done") || input.equals("done") || input.equals("d"))
break;
inputs[i] = input;
i++;
}
for (int j = 0; j < i; j++) {
int length = inputs[j].length();
String reverse = "";
for (int k = length - i; k >= 0; k--) {
reverse = reverse + inputs[j].charAt(k);
}
System.out.print("\n" + reverse);
}
}
}
Current output
What am I doing wrong??

Iterate through the array, and reverse elements at every index.
This solution is time consuming but does your job
for (int j = 0; j < inputs.lenght; j++) {
int length = inputs[j].length();
char a;
String rev = "";
for(int i =0; i< length; i++){
a = inputs[j].charAt(i);
rev = a + rev;
}
System.out.println(rev);
}

*Try to use StringBuilder And use method reverse -- #Artur Todeschini
To add to what Artur said, an ArrayList of StringBuilders could do the trick quite well:
for(StringBuilder nextEntry : stringBuilderList)
{
nextEntry.reverse();
}
The enhanced for-loop will go through each entry in the ArrayList, and the StringBuilder's reverse will change the order of the letters.
EDIT TO SHOW FORMATTING
ArrayList<StringBuilder> stringBuilderList= new ArrayList<>();
*note. given that this is for a lab, its probably for learning purposes and using built-in classes that does all the work for you are usually not the intended solution. -- #experiment unit 1998X

Try to use StringBuilder
And use method reverse

This is another "ArrayList and StringBuilder-less" version.
Create two Strings, one filled and one empty:
String nextString = stringArray[i],
template = new String();
Loop through the length of the String, adding the next character in from the end each time through.
int length = nextString.length() - 1;
for(int j = 0; j < length; j++)
{
template += nextString.charAt(length - j);
}
Add the whole String to the String array's index
stringArray[i] = template;
NOTE
This is an inner loop for a String array and is NOT complete code

Problems with iterated nextLine function

I am trying to use user inputted N lines of N characters to do some operations with. But first I need to know N and another int being inputted. When I define N and the other integer K and then write 5 lines (in this case) of 5 characters each the program runs well. But when I use the represented String a (which I then would split into 2 ints, N and K, not shown here to not complicate things), an error occurs. Even if I now input 6 lines, being the 5 last of 5 characters each, the program gives an error of no line found for the multi function. I don't understand what's the problem, and if I remove the string a and just define N and K the program runs well. What's more surprising, the program runs if I use an interactive console instead of text input and write the terms one by one.
static String [][] vetor (int N) {
Scanner scan = new Scanner(System.in);
String[][] multi = new String [N][N];
for (int i = 0 ; i<N ; i++){
String forest = scan.nextLine();
String[] chars = forest.split("");
for (int k=0; k<N; k++){
multi[i][k]= chars [k];
}
}
return multi;
}
public static void main(String args[]) {
Scanner scan = new Scanner(System.in);
String a = scan.nextLine();
int N = 5;
int K = 5;
String [][] multi = vetor(N);
I've tried many things, but I can't make sense of this. I didn't find any similar questions, but feel free to redirect me to an explanation.
Edit: This is a similar program one can run (with a possible input down (K<= N)) :
import java.util.Scanner;
import java.util.Arrays;
public class Main {
static int[] numerificar() {
Scanner myObj = new Scanner(System.in);
String Input = myObj.nextLine();
String[] Inputs = Input.split(" ", 0);
int size = Inputs.length;
int [] a = new int [size];
for(int i=0; i<size; i++) {
a[i] = Integer.parseInt(Inputs[i]);}
return a;
}
static String [][] vetor (int N) {
Scanner scan = new Scanner(System.in);
String[][] multi = new String [N][N];
for (int i = 0 ; i<N ; i++){
String forest = scan.nextLine();
String[] chars = forest.split("");
for (int k=0; k<N; k++){
multi[i][k]= chars [k];
}
}
return multi;
}
public static void main(String args[]) {
Scanner scan = new Scanner(System.in);
int[] a = numerificar();
int N = a[0];
int K = a[1];
int cadeira = 0;
String [][] multi = vetor(N);
for (int i = 0 ; i<N ; i++){
if (cadeira == 1) {
break;
}
for (int k=0; k<N-K+1; k++){
if (cadeira == 1) {
break;
}else if( multi[i][k].equals(".")){
for (int j=0; j<K; j++){
if(multi[i][k+j].equals( "#")){
k+=j;
break;
} else if (j == K-1) {
cadeira = 1;
}
}
}
}
}
System.out.println(cadeira);
}
}
5 3
.#.##
#####
##...
###..
#####
The output should be 1 in this case.

The problem is you are creating more than one Scanner that reads from System.in. When data is readily available, a Scanner object can read more data than you ask from it. The first Scanner, in the numerificar() method, reads more than the first line, and those lines are not available to the second Scanner, in the vetor() method.
Solution: use just one Scanner object in the whole program.
public class Main {
static Scanner globalScanner = new Scanner(System.in);
static int[] numerificar() {
String Input = globalScanner.nextLine();
String[] Inputs = Input.split(" ", 0);

How do I make this output happen in java?

I'm a beginner and I want to output the following using a for loop and subscript and I'm not sure.
output:
Jamaica
amaica
maica
aica
ica
ca
a
What can I do, in order to achieve this output?

First: You need to loop for generating n line which is the length of array.
Second: You need to print the spaces with is same value as row - 1 number of times.
Second: You need to print character start from row - 1 number to the length of the string.
And the final solution will be:
public class MyClass {
public static void printStr(String str) {
int i,j;
for (i = 0; i < str.length();i++) {
for(j = 0; j < i; j++) {
System.out.print(" ");
}
for(j = i; j < str.length();j++) {
System.out.print(str.charAt(j));
}
System.out.println("");
}
}
public static void main(String args[]) {
MyClass.printStr("Jamaica");
}
}

I would use two regular expressions, the first to terminate the loop when the String is filled with white space. The second to replace the first non-white space character with a white space in the loop body (after printing the current String value). And, if it's possible the String might be empty you should guard against that. Like,
String s = "Jamaica";
if (!s.isEmpty()) {
while (!s.matches("\\s+")) {
System.out.println(s);
s = s.replaceFirst("\\S", " ");
}
}
Outputs (as requested)
Jamaica
amaica
maica
aica
ica
ca
a

public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String s = scan.next(); //input through scanner class
int len = s.length();
for(int i=0;i<len;i++){
for(int j=0;j<i;j++){
System.out.print(" ");
}
for(int j=i;j<len;j++){
System.out.print(s.charAt(j));
}
System.out.println("");
}
}
Hopefully that helps

Try following code:
StringBuilder country = new StringBuilder("Jamaica");
for(int i=0; i< country.length();i++){
if(i > 0)
{
for(int j=0;j<i;j++){
country.setCharAt(j,' ');
}
}
System.out.println(country);
}

Palindrome program debugging

The problem is fixed but I need help with creating a method for one of the pieces of code. Any inputs will be appreciated. I tried using void methods but it didn't work. I have highlighted where i want the code to be a method.
import java.util.*;
public class Finalpal {
public Finalpal() {
// TODO Auto-generated constructor stub
}
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
String word;
int len, counter = 0;
System.out.println("Enter your word");
word = scan.next();
word = word.toUpperCase();
len = word.length();
char array[] = new char[len];
char reverse[] = new char[len];
for (int i=0; i < len; i++)
{
array[i] = word.charAt(i);
}
for (int j=len-1; j>=0; j--)
{
array[counter] = word.charAt(j);
counter++;
}
// This part needs to be a method
for (int k = 0; k < len; k++)
{
if (array[k] != reverse[k])
{
System.out.println("Not a palindrome");
break;
}
if ((array[k] == reverse[k]) && (k == len -1))
{
System.out.println("It is a palindrome");
}
}
}
}

You are not filling in the reverse array
try
for (int j=len-1; j>=0; j--)
{
reverse[counter] = word.charAt(j);
counter++;
}

You have used array[counter] instead of reverse[counter]. You have never filled reverse array

There is a way of doing this without creating a reversed string to compare to the original...
If I knew the length of the string, I could make a loop that checked the characters on either end to see if they were the same and move inward:
[a] [b] [c] [b] [a]
Loop 0: a = a
Loop 1: b = b
Loop 2: c = c
Result: Palindrome!
Functions you need:
int len = String.length();
char c = String.charAt(int);

Array out of bounds in Java?

I'm trying to run this code but I keep getting an out of bounds error. This is just the sub class for the super class "Simpler." The user enters in a string then the string is broken down into a char array. The array should not be smaller than the string yet I am getting this error. Can you tell me what I'm doing wrong? Thanks!
import java.util.*;
public class Encrypt extends Simpler
{
public void encryption()
{
boolean loop = true;
while(loop==true)
{
Scanner scan = new Scanner(System.in);
System.out.println("Please enter the phrase you'd like to encrypt: ");
String inPhrase = scan.nextLine();
char[] chars = inPhrase.toCharArray();
char tempArray[] = new char[chars.length+1];
tempArray = chars;
chars = new char[tempArray.length];
for (int i = inPhrase.length(); i<inPhrase.length(); i--)
{
if(chars[i]=='a')
{
chars[i]='1';
}
else if(chars[i]=='b')
{
chars[i]='2';
}
else if(chars[i]=='c')
{
chars[i]='3';
}
else if(chars[i]=='d')
{
chars[i]='4';
}
else if(chars[i]=='z')//I skipped some lines here for convienence
{
chars[i]='{';
}
else if(chars[i]==' ')
{
chars[i]='}';
}
}
String outPhrase = new String(chars);
System.out.println(outPhrase);
}
}
}

I think your for loop statement should look like this:
for (int i = 0; i < inPhrase.length(); i++)
if you're counting up, and like this:
for (int i = inPhrase.length() - 1; i >= 0; i--)
if you're counting down.
update
On looking back over it, I think there is more to it than that though.
I think your code needs to be rewritten:
String inPhrase = scan.nextLine();
char[] chars = inPhrase.toCharArray();
char tempArray[] = new char[chars.length()];
for (int i = 0; i < chars.length(); i++)
{
if(chars[i]=='a')
{
tempArray[i]='1';
}
.
.
.
.
}
String outPhrase = new String(tempArray);

No stop condition in the for loop, in this line:
for (int i = inPhrase.length(); i<inPhrase.length(); i--)
i gets 1, 0, -1, ... and wouldn't stop if -1 wouldn't throw an out of bounds exception

In for loop just changing the condition from i < inPhrase.length() to i >= 0 will do the job.

First thing:
for (int i = inPhrase.length(); i<inPhrase.length(); i--)
you never enter your loop because you assign i = n & entry condition is i < n.
it should be
for (int i = inPhrase.length()-1; i>=0; i--)
Now, this also removes your arrayoutofbound exception because earlier, you tried to access chars[n] which is actually the n+1 th character of that array.