Try the following:
int[][] multi = new int[5][10];
... which is a short hand for something like this:
int[][] multi = new int[5][];
multi[0] = new int[10];
multi[1] = new int[10];
multi[2] = new int[10];
multi[3] = new int[10];
multi[4] = new int[10];
Note that every element will be initialized to the default value for int, 0, so the above are also equivalent to:
int[][] multi = new int[][] {
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
};
... or, more succinctly,
int[][] multi = {
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
};
Answer from obataku on Stack OverflowTry the following:
int[][] multi = new int[5][10];
... which is a short hand for something like this:
int[][] multi = new int[5][];
multi[0] = new int[10];
multi[1] = new int[10];
multi[2] = new int[10];
multi[3] = new int[10];
multi[4] = new int[10];
Note that every element will be initialized to the default value for int, 0, so the above are also equivalent to:
int[][] multi = new int[][] {
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
};
... or, more succinctly,
int[][] multi = {
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
};
We can declare a two dimensional array and directly store elements at the time of its declaration as:
int marks[][]={{50,60,55,67,70},{62,65,70,70,81},{72,66,77,80,69}};
Here int represents integer type elements stored into the array and the array name is 'marks'. int is the datatype for all the elements represented inside the "{" and "}" braces because an array is a collection of elements having the same data type.
Coming back to our statement written above: each row of elements should be written inside the curly braces. The rows and the elements in each row should be separated by a commas.
Now observe the statement: you can get there are 3 rows and 5 columns, so the JVM creates 3 * 5 = 15 blocks of memory. These blocks can be individually referred ta as:
marks[0][0] marks[0][1] marks[0][2] marks[0][3] marks[0][4]
marks[1][0] marks[1][1] marks[1][2] marks[1][3] marks[1][4]
marks[2][0] marks[2][1] marks[2][2] marks[2][3] marks[2][4]
NOTE:
If you want to store n elements then the array index starts from zero and ends at n-1.
Another way of creating a two dimensional array is by declaring the array first and then allotting memory for it by using new operator.
int marks[][]; // declare marks array
marks = new int[3][5]; // allocate memory for storing 15 elements
By combining the above two we can write:
int marks[][] = new int[3][5];
I highly recommend you stick with using the for-loop for initialization of arrays with primitive values. My recommendation is stronger in the case of a multidimensional array.
However, here is the way:
int a = 4; // Number of outer array elements
int b = 2; // Number of inner array elements
int[][] board = IntStream
.range(0, a) // iterate 0..3
.mapToObj(i -> IntStream.range(0, b) // for each iteratoe 0..1
.map(j -> 1 + (i + (a + 1) * j)) // calculate the value
.toArray()) // compose the inner array
.toArray(int[][]::new); // compose the outer array
Note that the IntStream is able to create an array of primitives since it is a sequence of primitive int-valued elements. its method IntStream::toArray reutrns int[].
The composition of the outer array is a bit tricky since int[] is no longer a primitive value but an array itself. There is needed to use a method IntStream::mapToObj which maps int to an object - then the Stream<int[]> is returned and the method Stream::toArray(IntFunction<A[]> generator) converting to array with parameter has to be used since you cannot convert Object[] to int[][].
The parameter passed is simple. int[][]::new is nothing different than i -> new int[a][b].
Use IntStream. This will create a continuous stream of integers from 0 inclusive to n exclusive. So for a 3 x 3 matrix, the IntStream is 0, 1, 2.
make another IntStream for each integer in the outer stream from 0 to number of columns - also 3.
You cannot increment v in a stream because it must be "effectively final". Instead we use the equation board[j][i] = 1 + (j + m * i) which is effectively the similar to computing the index of the value if you were to flatten board into a single array (1D matrix).
import java.util.stream.IntStream;
import java.util.Arrays;
class J {
public static void main(String[] args) {
int n = 4;
int m = 2;
// n x m matrix
int[][] board = new int[n][m];
// Cols (m)
IntStream.range(0, m).forEach( i -> {
// Rows (n)
IntStream.range(0, n).forEach( j -> {
// Multiply i by row count
// to account for the row we are in
board[j][i] = 1 + (j + n * i);
});
});
System.out.println(Arrays.deepToString(board));
}
}
Output:
[[1, 5], [2, 6], [3, 7], [4, 8]]
Note: Just because streams allow you to write a neater, functional programming-like syntax, there is often times an associated performance toll. It stresses the idea, "why fix what's not broken?". For a 3 x 3 board, you probably won't see a difference. But, if your board were a lot larger, it probably won't prove itself to be worth it, considering all the objects created and extra space used behind the scene. Sometimes a simple for-loop (especially when working with arrays) is better.
Remember, simplicity is key.
You would use
List<List<String>> listOfLists = new ArrayList<List<String>>();
And then when you needed to add a new "row", you'd add the list:
listOfLists.add(new ArrayList<String>());
I've used this mostly when I wanted to hold references to several lists of Point in a GUI so I could draw multiple curves. It works well.
For example:
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.Stroke;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
@SuppressWarnings("serial")
public class DrawStuff extends JPanel {
private static final int PREF_W = 400;
private static final int PREF_H = PREF_W;
private static final Color POINTS_COLOR = Color.red;
private static final Color CURRENT_POINTS_COLOR = Color.blue;
private static final Stroke STROKE = new BasicStroke(4f);
private List<List<Point>> pointsList = new ArrayList<List<Point>>();
private List<Point> currentPointList = null;
public DrawStuff() {
MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
addMouseListener(myMouseAdapter);
addMouseMotionListener(myMouseAdapter);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setStroke(STROKE);
g.setColor(POINTS_COLOR);
for (List<Point> pointList : pointsList) {
if (pointList.size() > 1) {
Point p1 = pointList.get(0);
for (int i = 1; i < pointList.size(); i++) {
Point p2 = pointList.get(i);
int x1 = p1.x;
int y1 = p1.y;
int x2 = p2.x;
int y2 = p2.y;
g.drawLine(x1, y1, x2, y2);
p1 = p2;
}
}
}
g.setColor(CURRENT_POINTS_COLOR);
if (currentPointList != null && currentPointList.size() > 1) {
Point p1 = currentPointList.get(0);
for (int i = 1; i < currentPointList.size(); i++) {
Point p2 = currentPointList.get(i);
int x1 = p1.x;
int y1 = p1.y;
int x2 = p2.x;
int y2 = p2.y;
g.drawLine(x1, y1, x2, y2);
p1 = p2;
}
}
}
private class MyMouseAdapter extends MouseAdapter {
@Override
public void mousePressed(MouseEvent mEvt) {
currentPointList = new ArrayList<Point>();
currentPointList.add(mEvt.getPoint());
repaint();
}
@Override
public void mouseDragged(MouseEvent mEvt) {
currentPointList.add(mEvt.getPoint());
repaint();
}
@Override
public void mouseReleased(MouseEvent mEvt) {
currentPointList.add(mEvt.getPoint());
pointsList.add(currentPointList);
currentPointList = null;
repaint();
}
}
private static void createAndShowGui() {
JFrame frame = new JFrame("DrawStuff");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new DrawStuff());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
You can create a list,
ArrayList<String[]> outerArr = new ArrayList<String[]>();
and add other lists to it like so:
String[] myString1= {"hey","hey","hey","hey"};
outerArr .add(myString1);
String[] myString2= {"you","you","you","you"};
outerArr .add(myString2);
Now you can use the double loop below to show everything inside all lists
for(int i=0;i<outerArr.size();i++){
String[] myString= new String[4];
myString=outerArr.get(i);
for(int j=0;j<myString.length;j++){
System.out.print(myString[j]);
}
System.out.print("\n");
}