Java array size, length and loop examples

Java array size and length

Here are the most important concepts developers must know when they size Java arrays and deal with a Java array’s length:

  1. The theoretical maximum Java array size is 2,147,483,647 elements
  2. You can find the size of a Java array by querying an array’s length property
  3. The Java array size is set permanently when the array is initialized
  4. The size or length count of an array in Java includes both null and non-null characters
  5. Unlike the String and ArrayList, Java arrays do not have a size() or length() method, only a length property

How do you find the size of an array in Java?

You can determine the size of a Java array by querying its length property.

Here is an example of the size of a Java array being accessed in code:

int[] exampleArray = {1,2,3,4,5};
int exampleArraySize = exampleArray.length;
System.out.print("This Java array size is: " + exampleArraySize );
//The Java array length example prints out the number 5

Note that array length in Java is a property, not a method. That means the word length must not be followed by round brackets.

How do you size Java arrays?

To set the size of a Java array, you either explicitly state the intended capacity of the array when you initialize the array with the new keyword, as follows:

// Set the Java array size to three
int[] arraySizeExample = new int[3];

When the new keyword is used like this, the Java array size is permanently set, but all elements are initially set to null, or to zero if it is an array of primitive types.

Another way to size Java arrays is to provide all of the array elements at the time of initialization:

// Size the Java array with a set of known values
int[] arraySizeExample = new {0,1,1,2,3,5,8};

In this case, the size of the Java array is 7. You use the Java array’s length property to print out its size:

System.out.println("The Java array size is: " + arraySizeExample.length );

What is the maximum Java array size?

When you initialize Java arrays with the new keyword, the size argument is of type int.

The 32-bit Java int can go to a maximum of 2,147,483,647, so that is the theoretical maximum Java array size.

However, virtual machines for different operating systems may not allocate every bit on the into to the elements in the Java array, so maximum number of elements a Java array can hold is typically two or three bits less than the upper limit of a Java int.

Is the Java array size fixed?

In Java, once you set the Java array size it is fixed, and it can’t be changed.

This puts Java in sharp contrast to other programming languages like JavaScript where arrays resize dynamically. But in Java, one the array size is set, it can’t be changed.

However, there are collection classes in Java the act like a Java array but will resize themselves automatically.

Any class that extends the List interface will expand dynamically. But Java arrays do not expand and contract. The size of an array in Java can’t be changed once the array is initialized.

How is a Java array’s size and length used in a loop?

A common example of the Java array length property being used in code is a program looping through all of the elements in an array.

The following Java array length example prints out every number in an array named sequence:

int[] fibArray = {0,1,1,2,3,5,8};
for (int i=0; i  < fibArray.length; i++) {
  System.out.printlng(fibArray[i]);
}

What’s the difference between Java array size vs length?

In common parlance, when people want to know how many elements an array can hold, they use the term ‘size.’

However, Java arrays do not have a size() method, nor do they have a length() method. Instead, the property length gets a Java array’s size for you.

To further confuse matters, there any Java collection class that implements the List interface does have a size() method. So classes like Vector and Stack and ArrayList all have a size method. So to get the size of an ArrayList, you call its size method. But an Arraylist is very different when compared to a standard Java array.

To get the size of a Java array, you use the length property. To get the size of an ArrayList, you use the size() method.

Java array size length

Make sure you know the difference between the Java array length and the String’s length() method.

What’s the difference between Java array length vs length()?

When you put round brackets at the end of a word in Java, it indicates that you are calling a method.

Without round brackets, you are invoking a method.

The length property tells you the Java array size. It is not a method.

However, just to confuse matters, the String class does have a length() method. The length method of the String class tells you how any elements a String contains.

Developers often get the Java array length property confused with the Java String’s length() method. Confusing the two will result in a compile time error.

java array size

You find the Java array size through its length property, not the length() method.

How do I ask my boss for arrays?

I think you mean ‘a raise.’ That’s more of a professional development issue. But good luck.

I hope that if you do get arrays that it’s a sizeable one, and that your tenure with the company is lengthy.

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