NullPointer Exception

NPE

NullPointerException or NPE is an error every Java programmer is familiar with. This error holds the record for irritating programmers.

First, let's understand the concept of the null value for a string variable. When we create a string variable but forget to initialize, it acquires a null value. In comparison, if we don't initialize an int variable, it acquires a value of 0.

Let's consider an example of a string variable with a null value:

Main


              12345678
            
package com.example;

public class Main {
    public static void main(String[] args) {
        String string = null;
        System.out.println(string);
    }
}

As you can see, the output on the screen is null, and the code seems to be working. But let's now try using any method with a variable with the null value:

Main


              123456789
            
package com.example;

public class Main {
    public static void main(String[] args) {
        String string = null;
        string.toLowerCase();
        System.out.println(string);
    }
}

When attempting to call any method on a string variable with a null value, we receive a NullPointerException.

You might think this error is not so serious, but later, when you receive values not written by you personally, you may often come across it. Therefore, it is crucial to understand how to resolve this error now.

Ways to avoid NPE:

Be attentive. If you create a string variable, double-check if you have initialized it;
Use a null check before using the variable, for example:

Main


              123456789101112
            
package com.example;

public class Main {
    public static void main(String[] args) {
        String string = null;
        if (string == null) { //null check
            System.out.println("Can't use methods with string, because value is null");
        } else {
            System.out.println(string);
        }
    }
}

Tarefa

Swipe to start coding

I have a string array, and I'm trying to print it using a for-each loop, but I keep encountering an error that's already bothering me. Resolve this issue so that the data from my array will be displayed on the screen.

Solução

solution

Mude para o desktop para praticar no mundo realContinue de onde você está usando uma das opções abaixo

Tudo estava claro?

Obrigado pelo seu feedback!

Seção 5. Capítulo 5

NullPointer Exception

NPE

NullPointerException or NPE is an error every Java programmer is familiar with. This error holds the record for irritating programmers.

Let's consider an example of a string variable with a null value:

Main


              12345678
            
package com.example;

public class Main {
    public static void main(String[] args) {
        String string = null;
        System.out.println(string);
    }
}

As you can see, the output on the screen is null, and the code seems to be working. But let's now try using any method with a variable with the null value:

Main


              123456789
            
package com.example;

public class Main {
    public static void main(String[] args) {
        String string = null;
        string.toLowerCase();
        System.out.println(string);
    }
}

When attempting to call any method on a string variable with a null value, we receive a NullPointerException.

Ways to avoid NPE:

Be attentive. If you create a string variable, double-check if you have initialized it;
Use a null check before using the variable, for example:

Main


              123456789101112
            
package com.example;

public class Main {
    public static void main(String[] args) {
        String string = null;
        if (string == null) { //null check
            System.out.println("Can't use methods with string, because value is null");
        } else {
            System.out.println(string);
        }
    }
}

Tarefa

Swipe to start coding

Solução

solution

Mude para o desktop para praticar no mundo realContinue de onde você está usando uma das opções abaixo

Tudo estava claro?

Obrigado pelo seu feedback!

Seção 5. Capítulo 5

Mude para o desktop para praticar no mundo realContinue de onde você está usando uma das opções abaixo