If you create an array and declare its size, can I then change the size later if I under estimate how big I need it?

Question

If you create an array and declare its size, can I then change the size later if I under estimate how big I need it?

Answer 1

In classic array like:
int[] a = new int[3];
int[] b = new int[] {1,2,3,4,5};

you can assign new array to the same variable but old values will be lost;
a[0] = 100;
a = new int[6]; //old a[] with value 100 is lost
b = new int[6];
System.out.println( "a="+Arrays.toString(a)); // a=[0, 0, 0, 0, 0, 0]
System.out.println( "b="+Arrays.toString(b)); // b=[0, 0, 0, 0, 0, 0]

but you can create a new array and copy old array there.
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ArrayList<>() :
More comfortable is ArrayList<>(), where you can .add() elements over its size and array rises automatically.

Or you can increase size with .addAll(). Its adds group of elements in one assign.
ArrayList<String> als = new ArrayList<>(List.of("AB","CD","EF") ); // initialize

// increase to new size
als.addAll( Collections.nCopies(3, null) ); // newsize = size + 3
System.out.println( "als="+als); // als=[AB, CD, EF, null, null, null]
System.out.println( "als.size()="+als.size()+"\n"); // als.size()=6

// decrease size
int newSize = 3;
als.subList(newSize, als.size() ).clear();
System.out.println( "als="+als); // als=[AB, CD, EF]
System.out.println( "als.size()="+als.size()); // als.size()=3
// optionaly you can optimize memory after it with:
als.trimToSize();

Answer 2

You can't do that with a normal array, but you can use ArrayLists (part of the java.util package).
https://www.geeksforgeeks.org/arraylist-in-java/amp/

Answer 3

Thanks

Answer 4

Thanks