php Static关键字静态变量的实用方法(1/3)
代码如下 | 复制代码 |
class Foo { public static $my_static = 'foo'; public function staticValue() { return self::$my_static; } } class Bar extends Foo { public function fooStatic() { return parent::$my_static; } } print Foo::$my_static . " "; $foo = new Foo(); print $foo->staticValue() . " "; print $foo->my_static . " "; // Undefined "Property" my_static print $foo::$my_static . " "; $classname = 'Foo'; print $classname::$my_static . " "; // PHP 5.3.0之后可以动态调用 print Bar::$my_static . " "; $bar = new Bar(); print $bar->fooStatic() . " "; ?> |

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The role and usage of static in C language: 1. Variable scope; 2. Life cycle; 3. Internal function; 4. Modify global variables; 5. Modify function; 6. Other uses; Detailed introduction: 1. Variable scope, when If there is the static keyword before a variable, then the scope of the variable is limited to the file in which it is declared. In other words, the variable is a "file-level scope", which is very useful for preventing the "duplicate definition" problem of variables; 2. Life cycle, static variables are initialized once when the program starts executing, and destroyed when the program ends, etc.

1. static Please look at the following program first: publicclassHello{publicstaticvoidmain(String[]args){//(1)System.out.println("Hello, world!");//(2)}} Have seen this Segment programs are familiar to most people who have studied Java. Even if you have not learned Java but have learned other high-level languages, such as C, you should be able to understand the meaning of this code. It simply outputs "Hello, world" and has no other use. However, it shows the main purpose of the static keyword.

Practical application scenarios and usage skills of the static keyword in C language 1. Overview static is a keyword in C language, used to modify variables and functions. Its function is to change its life cycle and visibility during program running, making variables and functions static. This article will introduce the actual application scenarios and usage techniques of the static keyword, and illustrate it through specific code examples. 2. Static variables extend the life cycle of variables. Using the static keyword to modify local variables can extend their life cycle.

The functions of static: 1. Variables; 2. Methods; 3. Classes; 4. Other uses; 5. Multi-threaded environment; 6. Performance optimization; 7. Singleton mode; 8. Constants; 9. Local variables; 10. Memory Layout optimization; 11. Avoid repeated initialization; 12. Use in functions. Detailed introduction: 1. Variables, static variables. When a variable is declared as static, it belongs to the class level, not the instance level, which means that no matter how many objects are created, only one static variable exists, and all objects share this Static variables and so on.

Modifier abstract (abstract) 1. Abstract can modify a class (1) The class modified by abstract is called an abstract class (2) Syntax: abstractclass class name {} (3) Features: Abstract classes cannot create objects separately, but they can be declared Reference the abstract class name reference name; (4) Abstract classes can define member variables and member methods (5) Abstract classes have constructors. When used to create subclass objects, jvm creates a parent class object by default; abstract constructor methods apply Applied when jvm creates parent class object. 2. Abstract can modify methods (1) The method modified by asbtract is called an abstract method (2) Syntax: access modifier abstract return value

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