instantiating an array of objects with constructors in java

[jimi_hendrix]

hi so i have my class square with a constructor...i want to pass different vaules into each one when i instantiate it...but after i declare the array how do i do this?

in C# it was someting along the lines of



squares[i] = new Square(25, 75, 50 50);


but i dont think that that is the case of java

[s3gfault]

I'm no expert in java, but i think that does work. The key is to have the array declared properly first


Square squares[] = new Square[NUM_OF_SQUARES];
squares[0] = new Square(12, 13, 14,15);

[Reiger]

IIRC the proper syntax is:


Square [] squares=new Square [] {
new Square(11),
new Square(12),
/* more constructor calling */
new Square(15)
};


Or equivalently:


int i, num_squares = NUM_OF_SQUARES;
Square [] squares = new Square [num_squares];
for(i=0;i<squares.length;i++) {
/* code which calculates params */
squares[i]=new Square(/* [result of code which calculate params] */);
}


EDIT: And this is assuming you have a public constructor Square(int) available; tailor the code to meet your needs.

[shadylookin]

hi so i have my class square with a constructor...i want to pass different vaules into each one when i instantiate it...but after i declare the array how do i do this?

in C# it was someting along the lines of



squares[i] = new Square(25, 75, 50 50);


but i dont think that that is the case of java

that's correct but if you try accessing an index that you haven't specifically initialized then you'll get a null pointer exception

for instance



public class SquareUser {
public static void main(String args[]) {
Square[] squares = new Square[100];
squares[10].getX();
}

}



will return a null pointer exception because you haven't specifically initialized squares at index 10.

if however you do


public class SquareUser {
public static void main(String args[]) {
Square[] squares = new Square[100];
squares[10] = new Square(18);
squares[10].getX();
}

}


it will work


For this reason I honestly prefer using the java.util.List when I'm using objects because then you won't have indexes that hold nothing and throw null pointer exceptions when you accidentally use them


import java.util.List;
import java.util.ArrayList;

public class SquareUser {
public static void main(String args[]) {
List<Square> squares = new ArrayList<Square>();
squares.add(new Square(10));
System.out.println(squares.get(0).getX());
}

}