Length and Length() in Java

When to use .length vs .length()

They're two completely different things.

.length is a property on arrays. That isn't a method call.

.length() is a method call on String.

You're seeing both because first, you're iterating over the length of the array. The contents of the array are String, and you want to add up all of their lengths, so you then call the length on each individual String in the array.

Difference between size and length methods?

size() is a method specified in java.util.Collection, which is then inherited by every data structure in the standard library. length is a field on any array (arrays are objects, you just don't see the class normally), and length() is a method on java.lang.String, which is just a thin wrapper on a char[] anyway.

Perhaps by design, Strings are immutable, and all of the top-level Collection subclasses are mutable. So where you see "length" you know that's constant, and where you see "size" it isn't.

What's the difference between length and length()?

.length;

directly accesses a field member.

.length();

invokes a method (i.e. an accessor) to access a field member.

in the case of String, this is to be expected since it's immutable.

Why Java's String has the method length() rather than property length (like an array?)

Because length() is defined in CharSequence interface, which is implemented by String. Interfaces can't define properties in Java. Also, this makes it more interchangeable with other types.

In many methods, you may rely only on CharSequence interface instead of a real String, then you can use an instance of CharBuffer, Segment, String, StringBuffer or StringBuilder in the call site.

See also: CharSequence documentation.

When to use length and when to use length()

length --- arrays (int[], double[], String[]) ---- to know the length of the arrays.

length() --- String related Object (String, StringBuilder etc)to know the length of the String

size() --- Collection Object (ArrayList, Set etc)to know the size of the Collection

as length is not a method its works on arrays not on objects.

size() is a method which work on collection frameworks as i said up there .

now String is not a direct array and also not a Collection that's why we also need a different one which is length().

When to use type.length-1; and type.length(); in java

You want to use oldArray.length usually in a for loop call, because as in your example,

for(int i = 0; i < oldArray.length; i++) {
    //Executes from i = 0 to i = oldArray.length - 1 (inclusive)
}

Notice how i goes from 0 up until oldArray.length - 1, but stops exacty at oldArray.length (and doesn't execute). Since arrays start at position 0 instead of 1, old.Array.length is a perfect fit for the number that i should stop at. If arrays started at position 1 instead, for loops would look something like this:

for(int i = 1; i <= oldArray.length; i++) {
    //Executes from i = 1 to i = oldArray.length (inclusive)
}

oldArray.length - 1 is usually to access the last element:

int[] oldArray = {1,2,3,4,5};
int lastElement = oldArray.length - 1; // 4
oldArray[lastElement] // returns last element, 5

Although this is usually when you would use length - 1 vs length, there are many other cases where you would also want one over the other, and thus there is no real specific answer. But don't worry, keep coding, you'll get this hang of this soon ;)

---

Related Topics