How to deal with NullPointerException in Java?

Java is a very popular programming language, but in the process of writing code, we often encounter various abnormal situations. Among them, NullPointerException is also a relatively common one. This article will introduce the causes and handling methods of NullPointerException.

1. Causes of NullPointerException

NullPointerException is one of the most common exceptions in Java. It usually occurs when using a null reference, that is, when the program tries to access an empty object. For example, when we define a reference variable but do not initialize it, the value of the reference variable will be automatically assigned to null. But if we try to call a method or property of the object pointed to by this reference variable, a NullPointerException will occur in the program.

2. Handling of NullPointerException

Since the occurrence of NullPointerException is caused by calling a method or property on a null reference variable, we need to do a good job in the process of writing the code. Reference judgment to avoid NullPointerException.

The following are some commonly used NullPointerException exception handling methods:

1. Use conditional judgment

We can use conditional judgment statements to determine whether a variable is empty to avoid NullPointerException. abnormal. For example:

if (str != null) {
   System.out.println(str.length());
}

In this example, we first determine whether str is empty. If not, call the length() method of str.

2. Use try-catch statement

Another way to handle NullPointerException exception is to use try-catch statement to catch the exception. For example:

try {
   System.out.println(str.length());
} catch (NullPointerException e) {
   System.out.println("字符串为空！");
}

In this example, if str is empty, the program will throw a NullPointerException and be captured by the catch statement, and then output a prompt message.

3. Use the Objects.requireNonNull() method

Java 7 introduces a new tool class Objects, which has a very convenient method Objects.requireNonNull(). This method can be used to check the validity of the parameters. If the parameters are empty, a NullPointerException will be thrown.

For example:

String str = null;
Objects.requireNonNull(str, "字符串不能为空！");

System.out.println(str.length());

In this example, if str is empty, the program will throw a NullPointerException and output a prompt message.

To sum up, we need to pay special attention to the handling of null reference variables during code writing to avoid NullPointerException exceptions. Using conditional judgment, try-catch statement or Objects.requireNonNull() method are relatively common processing methods. When the program encounters a NullPointerException exception, we need to carefully analyze the cause of the exception and then take appropriate measures to handle it.

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