1, static characteristics
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With loads and loads of class
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Takes precedence over the object exists
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All objects are shared classes
Example: Let the class students should share the same number of classes.
In fact, this feature is also telling us when to use static?
If a member variable is shared by all objects, then it should be defined as static.
For example:
* Drinking fountains (static modification)
* Cups (not static modification)
* Common static, non-static properties
2, static calls
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It can be invoked by class name
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In fact, it can call itself by its object name.
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Recommended to use the class name called.
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Static modified content in general we call it: related classes, class members
class Demo1_Static {
public static void main(String[] args) {
/*Person p1 = new Person(); //创建对象
p1.name = "苍老师"; //调用姓名属性并赋值
p1.country = "日本"; //调用国籍属性并赋值
Person p2 = new Person();
p2.name = "小泽老师"; //调用姓名属性并赋值
//p2.country = "日本"; //调用国籍属性并赋值
p1.speak();
p2.speak();*/
Person.country = "日本"; //静态多了一种调用方式,可以通过类名.
System.out.println(Person.country);
}
}
class Person {
String name; //姓名
static String country; //国籍
public void speak() { //说话的方法
System.out.println(name + "..." + country);
}
}-
Creating objects memory map
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Create static memory map
3, static precautions
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In the static method is not this keyword
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Static is loaded with class and load, this is with the creation of the object exists.
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Static object exists than before.
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Static methods can only access static member variables and static member methods
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Static methods:
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Member variables: You can only access static variables
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Member method: You can only access static member methods
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Non-static method:
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Member variable: can be static, it can also be non-static
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Member method: But is static member method can also be non-static member methods.
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Jot: Static can only access static.
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Static like extracting file. Non-static file is compressed.
class Demo2_Static {
public static void main(String[] args) {
//Demo d = new Demo();
//d.print1();
Demo.print2();
}
}
class Demo {
int num1 = 10; //非静态的成员变量
static int num2 = 20; //静态的成员变量
public void print1() { //非静态的成员方法,既可以访问静态的成员也可以访问非静态的
System.out.println(num1);
System.out.println(num2);
}
public static void print2() { //静态的成员方法
//System.out.println(this.num1);//静态的成员方法不能访问非静态的,错误: 无法从静态上下文中引用非静态 变量 num1
System.out.println(num2);
}
}
4 difference between static variables and member variables
Different [1] belongs
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Member variables: the object belongs, with the creation of an object exists
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Static variables: belongs to the class, also known as class variables, and loaded with the loaded class
[2] Different memory location
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Member variables: the existence of heap memory
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Static variables: the existence of a static area (shared area) method zone
[3] different memory load time
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Member variables: With the creation of the object exists, facing the disappearance of the object disappear
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Static variables: With the load and load class, with the disappearance of class disappear
[4] call different:
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Member variables: Object variable members
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Static variables: the class can be called by name. You can also call the object name, it is recommended to use the class name called.
class Demo3_Static {
public static void main(String[] args) {
//method(); //错误: 无法从静态上下文中引用非静态 方法 method()
Demo3_Static.print(); //在主方法中调用本类的静态方法,可以省略类名.,系统会默认加上
Demo3_Static d = new Demo3_Static(); //非静态方法在调用的时候必须创建对象调用
d.method();
}
public void method() {
System.out.println("Hello World!");
}
public static void print() {
System.out.println("Hello World!");
}
}