Lernen 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.

Aufgabe

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.

Lösung

War alles klar?

Danke für Ihr Feedback!

Abschnitt 1. Kapitel 34

single

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Swipe um das Menü anzuzeigen

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?

Aufgabe

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.

Lösung

Wechseln Sie zum Desktop, um in der realen Welt zu übenFahren Sie dort fort, wo Sie sind, indem Sie eine der folgenden Optionen verwenden

War alles klar?

Danke für Ihr Feedback!

Abschnitt 1. Kapitel 34

single