Examples of working with strings

1. Concatenation (merging strings)

There's this slick and simple thing that you can do with strings in Java: you can glue them together. This operation is called concatenation. Here's how we remember it: Con-Cat-en-Nation. It is often called "joining strings" or "combining strings".

To concatenate two lines, you use the + sign. It's very easy:

"value1" + "value2"

Examples:

String name = "Steve" + "Steve";

String city = "New York" + "Steve";

String message = "Hello! " + "Steve";

And, of course, you can join lots of strings at the same time, and you can also join strings and variables.

Examples:

String name = "Steve";
String city = "New York";
String message = "Hello!" + city + name + city;

In the last example, you can see that the text in the message is difficult to read, because it is missing spaces. To indicate one or more spaces, you just need to write them in code and then wrap them in double quotes. It's easier than it sounds:

" "

By the way, if you don't put any spaces between the quotes (i.e. you write two double quotes in a row), you get the so-called "empty string":

""

On the one hand, it seems we have a string. But on the other hand, when we display this string, nothing is displayed. And when we join it with other strings, nothing happens. It's kind of like a zero in addition, only for strings.

2

Task

New Java Syntax, level 2, lesson 4

Locked

Let's change the code

Change the program so that the variable name has the value "Amigo".

Open

2. Converting to a string

As mentioned above, Java developers have made sure that absolutely every variable, object, and expression in Java can be converted to the String type.

What's more, this happens automatically when we concatenate a String with some other type. Examples:

int a = 5;
String name = "Steve" + a;

int a = 5;
String city = a + "New York" + a;

int number = 10;
String code = "Yo";
String message = "Hello! " + number + code;

In all three instances, we calmly combined int and String variables, and the result is always a String.

Examples:

int a = 5;
String name = "1" + a;

int a = 5;
String city = a + "9" + a;

int number = 10;
String code = "10";
String message = "" + number + code;

The plus operations are executed from left to right, so the result may be somewhat unexpected. Example:

int a = 5;
String name = a + a + "1" + a;

3. Converting a string to a number

Converting a number to a string in Java is as easy as concatenating it to an empty string:

String str = "" + number;

But what if you need to convert a string to a number? Well, not every string can be converted to a number. But if the string consists only of numbers, then you can. There is a special method for this in the Integer class.

The corresponding statement looks like this:

int x = Integer.parseInt(string);

Where int x is the declaration of an x integer variable, and string is a string that represents a number (i.e. a string consisting of digits).

Examples:

String str = "123";
int number = Integer.parseInt(str);

int number = Integer.parseInt("321");

int number = Integer.parseInt("321" + 0);

int number = "321";

4. Converting an object/primitive to a string

To convert an instance of any Java class or any primitive data type to a string, you can use the String.valueOf() method:

public class StringExamples {
    public static void main(String[] args) {
        String a = String.valueOf(1);
        String b = String.valueOf(12.0D);
        String c = String.valueOf(123.4F);
        String d = String.valueOf(123456L);
        String s = String.valueOf(true);

        System.out.println(a);
        System.out.println(b);
        System.out.println(c);
        System.out.println(d);
        System.out.println(s);
        
        /*
        Output:
        1
        12.0
        123.4
        123456
        true
         */
    }
}

5. Some methods for working with strings

And finally, I would like to talk about several methods of the String class.

length() method

The length() method lets you get the length of a string, i.e. how many characters it contains.

Examples:

String name = "Rome";
int count = name.length();

int count = "".length();

String name = "Rom";
int count = (name + 12).length();

You can call these methods on anything whose type is String, even an expression:

(name + 12).length()

toLowerCase() method

The toLowerCase() method lets you convert all characters in a string to lowercase:

Examples:

String name = "Rom";
String name2 = name.toLowerCase();

String name = "".toLowerCase();

String name = "ROM123";
String name2 = name.toLowerCase();

toUpperCase() method

The toUpperCase() method lets you convert all characters in a string to uppercase:

Examples:

String name = "Rom";
String name2 = name.toUpperCase();

String name = "rom123";
String name2 = name.toUpperCase();

2

Task

New Java Syntax, level 2, lesson 4

Locked

A few more corrections

Change the program to display the following text: "Coding in Java". Use variables.

Open

2

Task

New Java Syntax, level 2, lesson 4

Locked

I'm 15 again!

Change the program so that the variable age has the value 15.

Open