When encountering null pointer exceptions, you should avoid them from the source rather than relying solely on try-catch. 1. Understand that it comes from the attributes or methods that access null objects, such as the method returns null or the object is not initialized. 2. Actively check null before use. Java 8 can use Optional to force null situations. 3. Use Objects.requireNonNull() and Objects.equals() to assist in judgment and comparison. 4. Develop defensive programming habits, avoid returning null, and use empty sets or annotations to prompt potential problems.
Encountering a null pointer exception (NullPointerException) is a very common problem in Java development. It usually happens when you try to access a property or method of an object that is null. To deal with it, the key is not to just try-catch, but to avoid it from the source.
1. Understand how NullPointerException comes from
The root of NullPointerException is simple: you call a method or property of a null object. for example:
String str = null; int length = str.length(); // NullPointerException will be thrown here
Common scenarios include:
- The method returns null, and it will be used directly without subsequent checks.
- The elements in the collection are null, no judgment is made during traversal
- Direct access to fields or methods before object is initialized
Understanding these sources helps prevent in advance when encoding.
2. Actively check the null value
The most direct way is to make null judgment before using the object:
if (str != null) {
System.out.println(str.length());
}Although it is a bit verbose to write, this is the most basic and effective way to do it. Pay special attention to methods that may be null.
If you are using Java 8 or above, you can use Optional to wrap the possible value of null, forcing developers to face the possibility of null.
Optional<String> optionalStr = Optional.ofNullable(getString()); optionalStr.ifPresent(System.out::println);
Note, however, that Optional does not completely replace null checking, it is more like a design reminder.
3. Use Objects tool class to assist in judgment
Java provides some tool classes to simplify null processing, such as Objects.requireNonNull() :
public void setName(String name) {
this.name = Objects.requireNonNull(name, "Name cannot be null");
}This method can immediately throw more explicit exception information when null is passed, rather than waiting for an error when subsequent operations are reported.
There are also methods like Objects.equals() that can also avoid exceptions because one of the objects is null:
if (Objects.equals(str1, str2)) {
// Safe comparison}4. Code specification and defensive programming
Good coding habits can greatly reduce the occurrence of NullPointerException:
- Try to avoid letting the method return null, you can consider returning empty collections, empty objects and other alternatives.
- For external incoming parameters, check whether they are null as soon as possible.
- Use annotations such as
@NonNullor IDE plugins to prompt potential null problems (Lombok, JSR 305, etc.)
For example, you can write this:
public List<String> getItems() {
return Collections.emptyList(); // is safer than returning null}Basically that's it. Handling NullPointerException is not complicated, but it is easy to ignore details. The key is to develop a habit and think about one more step when writing code, rather than wait until an error is reported during the runtime before troubleshooting.
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