How to solve null pointer exception

Null pointer exception solution: 1. Use if statement or ternary operator to check whether the object is empty; 2. Use safe call operator, before calling the object's method or accessing the object's properties, First check whether the object is empty; 3. Use assertions. You can use the assert statement to check whether the object is empty. If it is empty, throw an exception; 4. Use the Optional class to wrap the object to indicate that the object may be empty. ; 5. Avoid potential null pointer exceptions by adding null pointer checks, initializing objects, and rationally designing code logic.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Null Pointer Exception is a common runtime exception, which indicates that a reference to a null object is used in the program. When we try to operate on a null object, a NullPointerException is thrown.

Null pointer exception usually occurs in the following situations:

The object is not initialized: When we declare an object variable but do not allocate memory space for it, the reference of the object is NULL, if you try to operate on it, a NullPointerException will be thrown.

The object is destroyed: When we still operate on the object after it is destroyed, a null pointer exception will be thrown.

The reference of the object is null: When we set the reference of an object to null and then try to operate on it, a Null Pointer Exception is thrown.

In order to solve the null pointer exception, we can take the following methods:

Check whether the object is empty: Before using the object, check whether it is empty. You can judge by using if statement or ternary operator.

if (object != null) {
    // 对象不为空，进行操作
}

Use the safe call operator (?.): The safe call operator is a syntactic sugar that simplifies null pointer checking. It can be used when calling the object's method or accessing the object's properties. Before, check if the object is empty. If the object is null, null is returned without throwing a NullPointerException.

object?.method();
object?.property;

Using the safe call operator can avoid explicit null pointer checking and make the code more concise.

Using assertions: Assertion is a mechanism used to check the consistency of a program during the development and testing phases. You can use the assert statement to check whether the object is empty. If it is empty, an AssertionError exception is thrown.

assert object != null : "Object cannot be null";

In a production environment, assertions can be disabled to improve performance.

Use the Optional class: Optional is a class introduced in Java 8 for handling potentially null objects. It can be used to wrap an object to indicate that the object may be empty. Using the Optional class avoids explicit null pointer checks and provides a series of methods to handle potentially null objects.

Optional<Object> optional = Optional.ofNullable(object);
optional.ifPresent(obj -> {
    // 对象不为空，进行操作
});

The Optional class provides a variety of operation methods, such as orElse, orElseGet, orElseThrow, etc. You can choose the appropriate method according to specific needs to handle objects that may be empty.

Avoid potential null pointer exceptions: During the programming process, we should try to avoid null pointer exceptions. You can reduce the occurrence of null pointer exceptions by adding null pointer checks, initializing objects, and rationally designing code logic.

The key to solving null pointer exceptions is to perform null pointer checks and take appropriate measures to deal with null objects. Through reasonable code design and programming habits, null pointer exceptions can be effectively avoided and resolved, and the robustness and stability of the program can be improved.

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