Learn StringBuilder

What is StringBuilder?

StringBuilder is a utility class for manipulating and editing string objects.

StringBuilder provides its own methods, and creating a StringBuilder object is straightforward and intuitive.

Main.java


              1
            
StringBuilder builder = new StringBuilder();

Inside the parentheses, we can also pass a string value, and our StringBuilder variable will hold that value:

Main.java


              1
            
StringBuilder builder = new StringBuilder("c<>definity");

To print our value to the console, we need to use one of the StringBuilder methods. It's the toString() method, which converts the value of the StringBuilder to a String type value. Let's look at an example:

Main.java


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package com.example;

public class Main {
    public static void main(String[] args) {
        StringBuilder builder = new StringBuilder("c<>definity");
        String string = builder.toString();
        System.out.println(string);
    }
}

StringBuilder in Action

StringBuilder provides a rich set of methods, with one of the most valuable and frequently used being append(String str). This method allows us to add a specified string to the existing content of a StringBuilder object.

Let's examine a code example:

Main.java


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package com.example;

public class Main {
    public static void main(String[] args) {
        // Initializing the new `String` with value "Hello"
        String hello = "Hello"; 
        System.out.println("Our string before using an append() method: " + hello);
        // Initializing a new `StringBuilder` with value of our already initialized string
        StringBuilder builder = new StringBuilder(hello); 
        // Using `append()` method, adding a string world to our `StringBuilder`
        builder = builder.append(" world!");
        // Creating a new `String` variable that has a `StringBuilder` value
        String result = builder.toString();
        System.out.println("Our string after using an append() method: " + result);
    }
}

Why not Use the + Operator?

We prefer StringBuilder's append method because it avoids creating multiple temporary objects, improving performance when modifying content repeatedly. Using the + operator creates a new object each time, which is costly in memory and time. StringBuilder modifies content directly, making it more efficient for repeated changes.

Task

Swipe to start coding

You're building a product display for a webpage. Each product has a name and a price, and they are stored in a 2D array.
You need to format the entire list into a nicely structured string using a StringBuilder.

Create a method called buildProductList(String[][] products) that returns a formatted String.
Initialize a StringBuilder and append the header:
"Product List:\n"
Loop through the products array using a for-each loop.
For each product:
- Extract the name (product[0])
- Extract the price (product[1])
- Append a line to the StringBuilder in the format:
  ProductName - $Price\n
Return the full String from the StringBuilder.

Solution

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Thanks for your feedback!

Section 5. Chapter 6

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Swipe to show menu

What is StringBuilder?

StringBuilder is a utility class for manipulating and editing string objects.

StringBuilder provides its own methods, and creating a StringBuilder object is straightforward and intuitive.

Main.java


              1
            
StringBuilder builder = new StringBuilder();

Inside the parentheses, we can also pass a string value, and our StringBuilder variable will hold that value:

Main.java


              1
            
StringBuilder builder = new StringBuilder("c<>definity");

Main.java


              123456789
            
package com.example;

public class Main {
    public static void main(String[] args) {
        StringBuilder builder = new StringBuilder("c<>definity");
        String string = builder.toString();
        System.out.println(string);
    }
}

StringBuilder in Action

Let's examine a code example:

Main.java


              12345678910111213141516
            
package com.example;

public class Main {
    public static void main(String[] args) {
        // Initializing the new `String` with value "Hello"
        String hello = "Hello"; 
        System.out.println("Our string before using an append() method: " + hello);
        // Initializing a new `StringBuilder` with value of our already initialized string
        StringBuilder builder = new StringBuilder(hello); 
        // Using `append()` method, adding a string world to our `StringBuilder`
        builder = builder.append(" world!");
        // Creating a new `String` variable that has a `StringBuilder` value
        String result = builder.toString();
        System.out.println("Our string after using an append() method: " + result);
    }
}

Why not Use the + Operator?

Task

Swipe to start coding

Create a method called buildProductList(String[][] products) that returns a formatted String.
Initialize a StringBuilder and append the header:
"Product List:\n"
Loop through the products array using a for-each loop.
For each product:
- Extract the name (product[0])
- Extract the price (product[1])
- Append a line to the StringBuilder in the format:
  ProductName - $Price\n
Return the full String from the StringBuilder.

Solution

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Thanks for your feedback!

Section 5. Chapter 6

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