Java - Calculate String Length

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Let`s see how to calculate the length of a string in Java.

Strings length()` returns the length of the string.

// String.java
public int length()

Because it returns the length of a Unicode string, it can be used for strings in other languages as well.

Returns the length of a string as follows.

String str1 = "Hello";
String str2 = "안녕하세요";
String str3 = "こんにちは";

System.out.println(str1.length());
System.out.println(str2.length());
System.out.println(str3.length());

Output:

5
5
5

Trim String: subString()

If you want to limit the length of a string to 20, you can truncate the string with subString().

String str = "The length is equal to the number of 16-bit Unicode characters in the string.";
System.out.println("origin length() : " + str.length());

String subString = str.substring(0, 20);
System.out.println("substring : " + subString);
System.out.println("substring length() : " + subString.length());

Output:

origin length() : 77
substring : The length is equal
substring length() : 20

subString() takes two arguments and returns a string containing beginIndex and no endIndex. So the above code substring(0, 20) truncates the string from index 0 to 19 and returns it.

// String.java
public String substring(int beginIndex, int endIndex)

If you want to cut a string and append ..., you can paste it as follows. trim() is a method that trims whitespace in a string.

String str = "The length is equal to the number of 16-bit Unicode characters in the string.";
System.out.println("origin length() : " + str.length());

String subString = str.substring(0, 20);
subString = subString.trim() + "...";
System.out.println("substring : " + subString);
System.out.println("substring length() : " + subString.length());

Output:

origin length() : 77
substring : The length is equal...
substring length() : 22

Difference between length, length() and size()

size() is used to get the length of Collections such as List.

List<String> list = new ArrayList<>();
list.add("Apple");
list.add("Wiki");
System.out.println("List size : " + list.size());

Output:

List size : 2

length is used to get the length of an Array. Unlike Strings length()`, it is not a function.

As shown below, length can be used to find the length of an Array and length() can be used to find the length of a String.

String[] strArray = new String[] {
            "Apple", "Kiwi", "Cherry", "Peach", "Grape"};
System.out.println("Array length : " + strArray.length);

for (String str : strArray) {
    System.out.println("string : " + str);
    System.out.println("length() : " + str.length());
}

Output:

Array length : 5
string : Apple
length() : 5
string : Kiwi
length() : 4
string : Cherry
length() : 6
string : Peach
length() : 5
string : Grape
length() : 5

string length limit

If you want to discard strings that exceed a certain length, you can exclude them with an if statement as shown below.

String[] strArray = new String[] {
            "Apple", "Kiwi", "Cherry", "Peach", "Grape"};

for (String str : strArray) {
    if (str.length() <= 5) {
        System.out.println("string : " + str);
        System.out.println("length() : " + str.length());
    }
}

Output:

string : Apple
length() : 5
string : Kiwi
length() : 4
string : Peach
length() : 5
string : Grape
length() : 5

The above code can also be implemented using a Stream like this:

String[] strArray = new String[] {
            "Apple", "Kiwi", "Cherry", "Peach", "Grape"};

Arrays.stream(strArray)
        .filter((str) -> str.length() <= 5)
        .forEach((str) -> {
            System.out.println("string : " + str);
            System.out.println("length() : " + str.length());
        });

Output:

string : Apple
length() : 5
string : Kiwi
length() : 4
string : Peach
length() : 5
string : Grape
length() : 5

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