Error resolution

introduction

In Java programming,NullPointerExceptionis a common runtime error that indicates that the code tries to access or operate anullValue.is a direct statement of this error, which usually occurs when trying to call anullWhen an object's method or obtains its properties. This article will explore the cause of this error and provide several solutions.

1. Problem description

1.1 Error report example

Here is a sample code that could cause this error:

public class Main {
    public static void main(String[] args) {
        String str = null;
        (());
    }
}

When running the above code you will get the following error:

Exception in thread "main" : null
    at (:5)

1.2 Error report analysis

This error indicates thatmainIn the method, variablestrAssigned asnull, and then try to call()Method, this is not allowed becausenullObject has no length.nullis a special value that indicates that no object is referenced.

1.3 Solutions

To solve this problem, we need to make sure that the object is notnull. Here are some solutions.

2. Solution

2.1 Method 1: Check the null value

Check if the object isnull。

public class Main {
    public static void main(String[] args) {
        String str = null;
        if (str != null) {
            (());
        } else {
            ("String is null");
        }
    }
}

2.2 Method 2: Use the Optional class

Using Java 8OptionalClass packaging may benullObject of  .

import ;
public class Main {
    public static void main(String[] args) {
        String str = null;
        Optional<String> optionalStr = (str);
        (s -> (()));
    }
}

2.3 Method 3: Use safe method calls

Using Java 8 built-in methods, such asString::isEmpty, to safely check whether the string is empty.

public class Main {
    public static void main(String[] args) {
        String str = null;
        if (str != null && !()) {
            (());
        } else {
            ("String is null or empty");
        }
    }
}

2.4 Method 4: Initialize in the constructor

Make sure the object is initialized correctly in the object's constructor and avoid creatingnullObject.

public class StringHandler {
    private String value;
    public StringHandler(String value) {
         = value;
    }
    public int length() {
        if ( != null) {
            return ();
        } else {
            throw new NullPointerException("String value is null");
        }
    }
}

3. Other solutions

• Always check if the object isnull。
• Use the IDE or code editor's checking function to identify potentialnullCheck for errors.
• During the code review process, please pay attention to searching and may return.nullmethod call.

4. Summary

In this article, we discussThe cause of the error and several solutions are provided. By making sure to check whether the object isnull, we can avoid such mistakes.

This is the end of this article about error resolution. For more related content, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!