12. Array Basic Facts
The basics of one dimensional arrays.
The fundamentals:
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Create (make space for) an array:
int[] data = new int[50]; String[] names = { "Justyn", "Connor", "Leo", "Ellie" };
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Arrays in Java do not grow or shrink. There is no
+=
for arrays. -
The length of the
data
array isdata.length
. -
Arrays without
new
have no space created for them.int[] nums; int len = nums.length; // error, array is not made at all!! nums[0] = -1; // error, certainly no item 0
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Getting values from an array:
int first = data[0]; int last = data[data.length - 1];
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Setting values in an array:
data[0] = 10; data[1] = 50;
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Printing out an array.
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At start of program:
import java.util.*;
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When you want to print an array, use
Arrays.toString
:int[] e = {1,2,3}; String ee = Arrays.toString(e); System.out.println(ee);
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Miscellaneous
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Arrays are handled like Java Objects in memory. The name of the array is a reference to a block of memory where the array data is stored.
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You cannot use the
{10,30,90}
form of the initializer anywhere except the declaration of the object.int[] nums = {10,30,90}; // OK int[] bad; bad = {10,30,90}; // ERROR
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In that case, you need to make a new (unnamed) array before you assign it:
int[] decent; decent = new int[]{10,30,90};
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