Strings

Hello,

The string data type is used in Java to hold our text data. Strings are reference data types, not primitive in Java.

When putting the text data into the variable of the String type, we need to put it between the double quote.

Let's define a simple String.

String myText = "Coddy String";

After this definition, Java has created an object in the head for us with our String.

Since String is an object of reference data type, it includes methods built into us by Java API.

In Java, the (+) operator is used to combine two different Strings.

class Main {
    public static void main(String[] args) {
        String catOne = "Coddy";
        String catTwo = "Garfield";

        String catNames = catOne + " " + catTwo;
        System.out.println(catNames);
    }
}

In addition to the + operator, we can merge two different String with the concat method.

System.out.println(catOne.concat(catTwo));
//CoddyGarfield

Perhaps the most used of these is the length() method.

With these methods, we can see how many characters a string expression consists of.

class Main {
    public static void main(String[] args) {
        String myText = "Coddy String";
        System.out.println("total char:" + myText.length());
    }
}

Now, let's learn how to use the toUpperCase and toLowerCase methods.

class Main {
    public static void main(String[] args) {
        String catOne = "Coddy";
        String catTwo = "Garfield";
        System.out.println(catOne.toUpperCase());   // CODDY
        System.out.println(catTwo.toLowerCase());   // garfield
    }
}

If we want to search in a String, we will use the indexOf method.

In the example below, the character s was searched and it was found to be in the 7th row.

class Main {
    public static void main(String[] args) {
        String txt = "My cat is Coddy";
        System.out.println(txt.indexOf("s")); //7
    }
}

Here the following question may have come to mind. 

While strings are placed between double quotes, what do we do if we want to pass double quotes in our String as below?

String txt = "My cat is "Coddy"";

The above code contains syntax errors and is not compiled by the compiler. If we want to use double trunks inside a String expression, we need to use the backslash which is the escape character.

This character tells the compiler that it is a String expression and should be evaluated within the text.

class Main {
    public static void main(String[] args) {
        String txt = "My cat is \"Coddy\"";
        System.out.println(txt); //My car is "Coddy"
    }
}

When defining the string, we stated that it is a reference type, not a primitive. 

Now let's define two strings of the same value.

class Main {
    public static void main(String[] args) {
        String catOne = "Coddy";
        String catTwo = "Coddy";
        boolean status = catOne == catTwo;
        //status => false
    }
}

== operator performs value control for primitive variables. Object types such as String hold the address in memory, not the object itself.

When we define two objects, even if they have the same value, because they are in different areas in the memory, catOne and catTwo variables actually hold different addresses. That's why when we compare it with the == control it returns false.

Equals method is used to compare the values of two strings.

if(catOne.equals(catTwo)){
	//codeblock works
}

The Equals method is used to compare the values of two strings.

if(catOne.equals(catTwo)){
	//codeblock works
}

In the example above, the equals method will return true because it compares the data in the address, not the addresses of the objects.

In this section, we learned about Strings in Java. 

See you in the next lesson. 🥳