The static keyword is used in Java to modify variables, methods, and internal classes, and is at the class level rather than the instance level. 1. Static Variables are shared by all objects and are suitable for counter or constant definitions. It is better to define constants using public static final; 2. Static methods are called directly through the class name and cannot access non-static members. They are suitable for tool classes and factory methods; 3. Static blocks are executed once when the class is loaded and are used to initialize static resources or configurations; 4. Static inner classes do not rely on external class instances to improve encapsulation and performance. Reasonable use of static can optimize the code structure, but attention should be paid to memory management and thread safety issues.
The static keyword is a very common but misunderstood keyword in Java. It is mainly used to modify variables, methods and internal classes. Understanding its role can help you better organize your code structure and control resource access.
Simply put, something with static added belongs to the class itself, not the instance object of the class . This means that no matter how many objects are created, these static members have only one copy and can be accessed directly through the class name without instantiation.
1. Static Variables
Static variables are also called class variables. They do not belong to a certain object, but to the entire class. All objects of this class share the same static variable.
Applicable scenarios:
- Stores class-level status information, such as counters.
- Global configuration or constant definition.
public class Counter {
public static int count = 0;
public Counter() {
count ;
}
} In the example above, count will be incremented no matter how many Counter objects are created because it is static.
Recommended usage:
- Try to use
public static finalto define constants. - Avoid overuse of static variables, because they have a long life cycle and can easily cause memory waste or concurrency problems.
2. Static methods
Static methods can be called directly through the class name without creating objects. They cannot access non-static member variables or methods.
Applicable scenarios:
- Tool-class methods, such as
Math.sqrt(). - Factory method or auxiliary method.
public class Utils {
public static void printMessage(String msg) {
System.out.println(msg);
}
}Call method:
Utils.printMessage("Hello");Note:
-
thisorsupercannot be used in static methods. - Static methods can only access other static members.
3. Static Blocks
Static code blocks are used to initialize static variables, which are executed once the class is first loaded.
public class DBConfig {
public static String URL;
static {
URL = "jdbc:mysql://localhost:3306/mydb";
System.out.println("DB Config loaded.");
}
}This feature is suitable for some one-time initialization operations, such as reading configuration files, establishing connection pools, etc.
Common uses:
- Resource preparation when class loading.
- Initialize complex static structures.
4. Static Nested Classes
Java allows defining another class in one class, which is called a static nested class if static is added. It does not depend on instances of external classes.
public class Outer {
private static String name = "Outer";
static class StaticNested {
void display() {
System.out.println(name);
}
}
}How to use:
Outer.StaticNested nested = new Outer.StaticNested(); nested.display();
benefit:
- It can reduce coupling and improve packaging performance.
- More resource savings, because there is no need to hold references to external classes.
Overall, static is a useful tool, but it also needs to be used reasonably. Especially in multithreaded environments, be especially careful about the synchronization of static variables. Master it well and write clearer and more efficient code.
Basically that's it.
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