在不设置对象数的情况下用Java创建数组？

Question

I just started learning Java and found that you have to set number of objects in an array before hand. so how can I make an array withou setting number of objects in an array like done in objective c. I know I can do something like this

int a[] = {1,3,1,3,41,34} 

but in this case you have to put all the objects at once is there a way to do that?

thanks

Answer 1

Arrays in Java are not resizeable. If you need that kind of capability, you should look into the List<> interface, and the classes that implements it (including ArrayList<> , LinkedList<> , etc.)

Answer 2

You don't have to put all of the objects in, but at the very least you'll need to know how many objects you are going to put in, like so:

int[] a = new int[6];

If you need it to be dynamic you'll have to use a List, or something like it.

Answer 3

There are 3 ways to create an array in Java:

int[] a = new int[50];
int[] b = {1,2,3,4,5,6,7,8,9,10};
int[] c = new int[]{1,2,3,4,5,6,7,8,9,10};

If you want a resizable array check out ArrayList .

Answer 4

You'll have to use ArrayList<Integer> if you don't know the number of elements before-hand.

ArrayList<Integer> a = new ArrayList<Integer>();
a.add(1);
a.add(3);
...

Answer 5

Arrays have a fixed number of objects in them.

You can allocate them empty, with:

Object[] objects = new Object[100]; // 100 null objects

For a variable-length list, try List. like:

List<String> strings = new ArrayList<String>(); // arraylist is one of several kinds of list.

Answer 6

Like everyone else said, you will have to use lists.... Just wanted to add a little comparison to Objective-C(well Apples framework classes for objective-C but anyway)

Unlike in Obective-C where you can init NS(Mutable)Arrays and whatnot with a nil terminated list, in Java you cannot add default values to your lists when you create them, you have to repeatedly call the add method to add the objects. Java introduced a variable number of arguments in Java 1.5, but as of 6.0 has not added constructors that use this feature to any of their implementations of the List interface.

Answer 7

Check out the google guava library, specifically http://google-collections.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Lists.html . The lists class lets you create a mutable arraylist with initial elements in a one-liner.

Tangentially, the Guava libraries are very useful for common day-to-day collection type stuff. Check them out.