I am new to Java and I need to create a two dimensional array of boolean of which the dimensions of can be changed and then display the boolean table, but I am getting some errors.
I tried using the reccomended fixes but these made more errors
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner joos = new Scanner(System.in);
System.out.println("Please enter the desired height of the grid.");
int y = joos.nextInt();
System.out.println("Please enter the desired width of the grid.");
int x = joos.nextInt();
boolean [] [] height = new boolean[y][x];
//System.out.println(y);
//System.out.println(x);
int i = 0;
int j = y*x;
for (i<=j:i++;) {
System.out.println(height[i]);
}
}
}
There's a couple things going on here:
First, the statement for(i<=j; i++;) is not a valid way to create a for loop. Secondly, if i<j, but j=x*y, then you are going to get an ArrayIndexOutOfBoundsException when you call height[i] when i>=y.
If you want to do something for each position in your 2d array, you can use the following nested loops:
for (int i = 0; i < y; i++){
for (int j = 0; j < x; j++) {
// do something now with the boolean at height[i][j]
boolean value = height[i][j];
System.out.println(value);
}
}
The general idea here is that a 2d array requires a "2d" loop (in other words, 2 nested loops) to access each element.
Related
I'm trying to write a code where I need to use three methods. The first method must use a nested while loop to create a multidimensional array that is 3x3 and will get the values from the command line.
The second method needs top use nested for loops in order to calculate the average of the doubles in each row. And the final method needs to shows the result of those averages. I'm currently getting cannot final symbol error. What did I do wrong?
I created the method fillArray to have the values from the user be stored. The return value is all the values entered at the command line.
import java.util.Scanner;
public class Scorer {
public static void main(String[] args) {
fillArray();
System.out.println(scores);
}
public static double [][] fillArray(){
double [][] scores = new double [3][3];
Scanner scnr = new Scanner(System.in);
int col = 3;
int row = 3;
System.out.println("Enter your scores: ");
int i = 0;
while(i < scores[i].length){
int j = 0;
while(j < scores[i].length){
scores[i][j] = scnr.nextDouble();
j++;
}
i++;
}
return scores;
}
}
The code should allow for 3 values to be entered for each column and then be able to calculate the average of each rows values and have those results displayed back.
while(i < scores[i].length){
in the third interaction you will get a indexofboundsexception.
I = 3 -> scores[3].length
System.out.println(scores);
score was not declared in the main method.
System.out.println(scores);
I've never tested this, but you're trying to print a vector. don't know if this work
So I help tutor an Algebra 2 class at my local high school, and the class is currently looking over matrices. Though not there, they will eventually get to multiplication of matrices. After taking Computer Science last year and learning Java, the teacher I help thought I should try to write a program to multiple matrices.
At the moment, I have up to defining the numbers for the first array that holds the information for the first matrix. However, I have a small issue. As represented by this picture:
the line asking for the index integers is being repeated after already recording the integers. I assume this is due to my layered for loops, but I can't be for certain. Usually new eyes see problems clearer. Any who could help me would be appreciated.
Code:
package matrixmultiplication;
import java.util.*;
public class MatrixMultiplication {
public static void main(String[] args) {
System.out.println("What is the size of the first matrix?");
int matrix1Rows = matrixRows();
int matrix1Columns = matrixColumns();
int[] matrix1 = new int[matrix1Rows * matrix1Columns];
doubleSpace();
System.out.println("What is the size of the second matrix?");
int matrix2Rows = matrixRows();
int matrix2Columns = matrixColumns();
int[] matrix2 = new int[matrix2Rows * matrix2Columns];
doubleSpace();
if (matrix1Columns != matrix2Rows) {
System.out.println("These cannot be multiplied!");
System.exit(0);
} else {
matrix1Numbers(matrix1Rows, matrix1Columns);
}
}
public static int matrixRows() {
System.out.print("Rows:");
Scanner rowSc = new Scanner(System.in);
int rows = rowSc.nextInt();
return rows;
}
public static int matrixColumns() {
System.out.print("Columns:");
Scanner colSc = new Scanner(System.in);
int cols = colSc.nextInt();
return cols;
}
public static int[] matrix1Numbers(int rows, int cols) {
int[] numb = new int[rows * cols];
for (int j = 0; j <= numb.length; j += rows) {
for (int i = 1; i <= cols; i++) {
for (int k = 1; k <= rows; k++) {
System.out.println("What is the value for index ("
+ k + "," + i + ")?");
Scanner inp = new Scanner(System.in);
if (j + k <= numb.length) {
numb[j + k - 1] = inp.nextInt();
}
}
}
}
for (int i = 0; i < numb.length; i++) {
System.out.println(numb[i]);
}
return numb;
}
public static void doubleSpace() {
System.out.println();
System.out.println();
}
}
I use NetBeans 8.2 and the latest working version of Java for NetBeans.
I'm not familiar with the matrixmultiplication package, so I may be rambling here.
for (int j = 0; j <= numb.length; j += rows){
I'm not entirely sure what the outer for loop your have is for, but this most outer for loop causes you to ask for the values of the indices cols times more than you want.
I feel that you originally wanted to use this outer for loop to iterate through each row, and wasn't planning on having the second for loop iterating through cols perhaps?
Also, Kevin Anderson mentions this above. You might avoid this problem altogether if you return a double int array as opposed to storing all values in the matrix in a single dimension. I personally feel it would make more sense.
Just nitpicking, but I wouldn't make a new scanner every time you want to use one in a different method. You could just make a field at the top of your class, instantiate it once in your main method, and then pass it in as a parameter to all methods using the scanner.
I have an array a[5][5] and several values. I want to randomly assign values based on random percentages I create. For example one value is 6 and 25% of the elements in the array should have the value 6. With what I have so far: I created the random percentages and I'm able to randomly assign values for different elements in the array. My problem is: more than 25% of the elements have 6. My question is: How do I make sure that when assigning elements with 6, exactly 25% of the elements in the array a[5][5] have that value? I'm new to programming and tried several loops and ifs but nothing is working out for me. Please push me towards the right direction.
25% of 25 is about 6. It is not accurate. Here is a possible solution.
import java.util.Random;
import java.util.Scanner;
public class Matrix25 {
public static void main(String[] args) {
int[][] Matrix = new int[5][5];
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the number you want to fill the array to 25%: ");
int number = scanner.nextInt();
int percentage=25;
generateMatrix(Matrix,number,percentage);
printMatrix(Matrix);
}
public static void generateMatrix(int Matrix[][],int num, int perc) {
int n;
int max=Matrix.length*Matrix[0].length;
int[] numbers = new int[max];
Random rnd = new Random();
int m = (int)(max * (perc/100.0));
int x=num>m?m-1:m;
for(int i=0;i<max;i++)
numbers[i]=(i<x)?num:i+1;
for(int i=0;i<Matrix.length;i++)
for(int j=0;j<Matrix[i].length;j++) {
n=rnd.nextInt(max);
Matrix[i][j]=numbers[n];
numbers[n]=numbers[max-1];
max--;
}
}
public static void printMatrix(int Matrix[][]) {
for(int i=0;i<Matrix.length;i++) {
for(int j=0;j<Matrix[i].length;j++)
System.out.printf("%3d\t",Matrix[i][j]);
System.out.print("\n");
}
}
}
I would do it like this
import java.util.Random;
import java.util.Scanner;
class Random2darray {
/**
* #param args
*/
public static void main(String[] args) {
// Create array; you specified 5x5 but you probably shouldn't hard code like this
int[][] numbers = new int[5][5];
//Create a scanner to get user input
Scanner scanner = new Scanner(System.in);
//I am not doing anything to make sure they give a decimal so the program won't work
//right if you are not giving a decimal
System.out.println("How much do you want to fill? Enter a decimal.");
//Get a double
double populatePercentage = scanner.nextDouble();
System.out.println("What number do you want to fill with?");
//Get an int
int fillNumber = scanner.nextInt();
//Don't hardcode like this
int fillTimes = numberOfTimesToFill(25, populatePercentage);
//This is declared outside of the loops because otherwise it will be
//reset each time the loop runs
int count = 0;
//Create a random number generator; default seed is current time which is good enough for this
Random rand = new Random();
//Fill the array with numbers
for (int i = 0; i < 5; i++) {
for (int j = 0; j < 5; j++) {
//Check if you have filled with given number enough times
if(count < fillTimes){
numbers[i][j] = fillNumber;
//Increment count by 1; this is how you are keeping track
count++;
}else{
//Otherwise pick a random number generator
//This will pick a random int between 0 - 50 inclusive
int randomNumber = rand.nextInt(51);
//This will make sure that you are not generating random numbers that are the same
//as the number you are filling with; This says if it is the same generate a new number
while(randomNumber == fillNumber){
randomNumber = rand.nextInt(51);
}
//Once we know its random fill the spot in the array
numbers[i][j] = randomNumber;
}
}
}
//Print the array out
printArray(numbers);
}
private static void printArray(int[][] numbers) {
//Just loop through and print every number
for (int i = 0; i < 5; i++) {
for (int j = 0; j < 5; j++) {
//Print with formatting: this says print a digit (%d) followed by a
//tab(\t) and then specifies what number I want to print
System.out.printf("%d\t", numbers[i][j]);
}
//Print a new line after each row
System.out.printf("\n");
}
}
private static int numberOfTimesToFill(int elements, double populatePercentage) {
System.out.println((int)(populatePercentage * elements));
//Cast to an int to truncate the decimal part of the number because you can't have
//a fraction of an element
return (int)(populatePercentage * elements);
}
}
I have commented the code to explain what everything does. However it does not protect against bad user input and it hardcodes the size of the array, you should always try to avoid hardcoding. In this example I did it (and marked where) to be more clear. Also as was mentioned in the comments above, for your situation where you want exactly 25% of 25 is not possible. This is because .25 * 25 = 6.25 and you can't have .25 of an element.
I have created this code (with the help of Reimeus). How would I achieve to instead of replace every value in the array with true to replace only one pre determined (by z for example) and this always being a value on the top column of the 2d array. Furthermore I would like to how I should start to get instead of the output being true and false it being x for true and y for false but still keeping the array an boolean
import java.util.*;
class Main {
public static void main(String[] args) {
int x;
int y;
Scanner scanner;
scanner = new Scanner(System.in);
x = scanner.nextInt();
y = scanner.nextInt();
boolean[][] cells = new boolean[x][y];
for (int i = 0; i < cells.length; i++) {
Arrays.fill(cells[i], true);
System.out.println(Arrays.toString(cells[i]));
}
}
}
Use Arrays.toString to display the array content, otherwise the Object#toString representation of the Object arrays will be displayed
System.out.println(Arrays.toString(cells[i]));
Aside from Reimeus answer:
What would I need to do if I would want to make only 1 piece of the array true and decide where this true should go in the same way as I decide the length of the array.
Using fact that boolean arrays are by default filled with false values you just need to read once index of element that should be set to true just like you did with lengths
boolean[][] cells = new boolean[x][y];
int trueX = scanner.nextInt();
int trueY = scanner.nextInt();
cells[trueX][trueY] = true;
also don't forget to remove Arrays.fill(cells[i], true);
Secondly is there a way in which I could replace the true statement with "*" and the false statement with "-"
You can create second loop that will iterate over elements of row and if it its value is true print * if not - like in this code:
for (int i = 0; i < cells.length; i++) {
for (int j = 0; j < cells[i].length; j++) {
if (cells[i][j])
System.out.print("* ");
else
System.out.print("- ");
}
System.out.println();
}
or just replace "true" string from result of Arrays.toString() with * and "false" with "-"
for (int i = 0; i < cells.length; i++) {
System.out.println(Arrays.toString(cells[i]).replace("true", "*")
.replace("false", "-"));
}
I'm trying to write a small program that prints out distinct numbers in an array. For example if a user enters 1,1,3,5,7,4,3 the program will only print out 1,3,5,7,4.
I'm getting an error on the else if line in the function checkDuplicate.
Here's my code so far:
import javax.swing.JOptionPane;
public static void main(String[] args) {
int[] array = new int[10];
for (int i=0; i<array.length;i++) {
array[i] = Integer.parseInt(JOptionPane.showInputDialog("Please enter"
+ "an integer:"));
}
checkDuplicate (array);
}
public static int checkDuplicate(int array []) {
for (int i = 0; i < array.length; i++) {
boolean found = false;
for (int j = 0; j < i; j++)
if (array[i] == array[j]) {
found = true;
break;
}
if (!found)
System.out.println(array[i]);
}
return 1;
}
}
The simplest way would be to add all of the elements to a Set<Integer> and then just print the contents of the Set.
First of all, the "else if" statement is incorrect, since you don't provide any condition to the if (if you want an if, you need to write "if (condition) ...").
Second, you cannot decide inside the inner loop, if a value should be printed: The way your code works you write a value array[i] for each value array[j] that is different from array[i]!
Third: the inner loop needs only to go from 0 to the outer index i-1: For each element, you need only to decide, if it is the first occurrence (i.e. if the same value occured at any previous index or not). If it is, print it out, if not, ignore it.
A proper implementation of CheckDuplicate() would be:
public static void checkDuplicate(int array []) {
for (int i = 0; i < array.length; i++) {
boolean found = false;
for (int j = 0; j < i; j++)
if (array[i] == array[j]) {
found = true;
break;
}
if (!found)
System.out.println(array[i]);
}
}
But of course, some kind of Set would be much more efficient for bigger arrays...
EDIT: Of course, mmyers (see comments) is right by saying, that since CheckDuplicate() doesn't return any value, it should have return type void (instead of int). I corrected this in the above code...
Put them in a set ordered by insertion time, then convert back to an array if necessary.
new LinkedHashSet<Integer>(array).toArray()
Try throwing all of the integers into a Set. Duplicates will not ever be added to the Set and you will be left will a set of unique integers.
What you want can be accomplished using Java collection API, but not exactly as an one-liner, due to fact collection methods work with Objects and not primitives. J2SE lacks methods that convert, say, int[] to Integer[], but Apache Commons Lang library contains such useful methods, like ArrayUtils.toObject() and ArrayUtils.toPrimitive().
Using them, method to remove duplicated elements from an integer array looks something like this:
public static int[] removeDuplicates(int... array) {
Integer[] ints = ArrayUtils.toObject(array);
Set<Integer> set = new LinkedHashSet<Integer>(Arrays.asList(ints));
return ArrayUtils.toPrimitive(set.toArray(new Integer[set.size()]));
}
If your application is likely to include more of array/collection manipulation, I suggest you take a look at that library, instead of implementing things from scratch. But, if you're doing it for learning purposes, code away!
It would probably be better to add each number to a Set implementation rather than an array. Sets are specifically for storing collections of elements where you want to filter out duplicates.
Either use a Set as other people have suggested or use an List compatible class. With a list compatible class just use the Contains method to check if it already exists in the array.
import java.util.Scanner;
public class PrintDistinctNumbers {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
int [] numberArray = createArray();
System.out.println("The number u entered are: ");
displayArray(numberArray);
getDistinctNumbers(numberArray);
}
public static int[] createArray() {
Scanner input = new Scanner(System.in);
int [] numberCollection = new int [10];
System.out.println("Enter 10 numbers");
for(int i = 0; i < numberCollection.length; i++){
numberCollection[i] = input.nextInt();
}
return numberCollection;
}
public static void displayArray(int[] numberArray) {
for(int i = 0; i < numberArray.length; i++){
System.out.print(numberArray[i]+" ");
}
}
public static void getDistinctNumbers(int[] numberArray) {
boolean isDistinct = true;
int temp = 0;
int [] distinctArrayNumbers = new int [10];
for ( int i = 0; i < numberArray.length; i++){
isDistinct = true;
temp = numberArray[i];
for( int j = 0; j < distinctArrayNumbers.length; j++){
if( numberArray[i] == distinctArrayNumbers[j] ){
isDistinct = false;
}
}
if(isDistinct){
distinctArrayNumbers[temp]=numberArray[i];
temp++;
}
}
displayDistinctArray(distinctArrayNumbers);
}
public static void displayDistinctArray(int[] distinctArrayNumbers) {
for( int i = 0; i < distinctArrayNumbers.length; i++){
if(distinctArrayNumbers[i] != 0){
System.out.println(distinctArrayNumbers[i]);
}
}
}
}