1、static修饰变量

package CommonClass;public class StudentStaticx {private int id;private String name;private int age;public static String room;private static int idcounter=0;public StudentStaticx(){this.id=++idcounter;}public StudentStaticx(String name,int age){this.name=name;this.age=age;this.id=++idcounter;}public void setName(String name) {this.name = name;}public void setAge(int age) {this.age = age;}public String getName() {return name;}public int getAge() {return age;}public int getId() {return id;}public static int getIdcounter() {return idcounter;}public void setId(int id) {this.id = id;}public static void setIdcounter(int idcounter) {StudentStaticx.idcounter = idcounter;}
}

package api_demo;import CommonClass.StudentStaticx;/*
* 如果一个成员变量使用了static关键字，那么这个变量不再属于对象自己，而是输入所在的类
* 多个对象共享共一份数据
* */
public class DemoStaticFiled {public static void main(String[] args) {StudentStaticx one = new StudentStaticx("jinfl",17);System.out.println(one.getName()+"*"+one.getAge());StudentStaticx two = new StudentStaticx("haolh",16);System.out.println(two.getName()+"*"+two.getAge());one.room = "1705";System.out.println(one.getName()+"*"+one.getAge()+"**"+one.room+"*"+one.getId());System.out.println(two.getName()+"*"+two.getAge()+"**"+two.room+"*"+two.getId());}
}

"C:\Program Files\Java\jdk-14.0.1\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\lib\idea_rt.jar=2615:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\Jinfanglin\IdeaProjects\javaSe\out\production\javaSe api_demo.DemoStaticFiled
jinfl*17
haolh*16
jinfl*17**1705*1
haolh*16**1705*2Process finished with exit code 0

2、static修饰方法

package CommonClass;public class Myclass {public void method(){System.out.println("普通方法");}public static void methodStatic(){System.out.println("静态方法");}
}

package api_demo;import CommonClass.Myclass;/*
* 一旦使用static修饰成员方法，那么这就成为了静态方法，静态方法不属于对象，而是属于类
* 如果没有static关键字，必须创建对象后才能通过对象使用
* 如果有了static关键字，不需要创建类对象，就可以直接使用
* 对于本类当中的静态方法，可以省略类名称
* 注意事项：
* 1、静态不能直接访问非静态
* 原因：内存中先有的静态，再有的非静态。
* 2、静态方法当中不能写this,this代表当前对象。
*
* */
public class StaticMethod {public static void main(String[] args) {Myclass obj=new Myclass();obj.method();obj.methodStatic();// 正确不推荐，这种写法在被编译后，也会自动转为会类名称.方法名Myclass.methodStatic();//正确推荐}
}

"C:\Program Files\Java\jdk-14.0.1\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\lib\idea_rt.jar=3758:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\Jinfanglin\IdeaProjects\javaSe\out\production\javaSe api_demo.StaticMethod
普通方法
静态方法
静态方法Process finished with exit code 0

3、静态代码块

package CommonClass;public class Person {private String name;private int age;static{System.out.println("静态代码块");}public Person(){}public Person(String name, int age){this.name = name;this.age = age;}public String getName() {return name;}public int getAge() {return age;}public void setName(String name) {this.name = name;}public void setAge(int age) {this.age = age;}
}

package api_demo;
import CommonClass.Person;
/** 静态代码块格式：* public class leimign{*  static{*  // 静态代码块的内容* }* }* 特点：当第一次用到本类的时候，静态代码块执行唯一的一次* 静态内筒总是优先于非静态* */
public class staticCode {public static void main(String[] args) {Person one = new Person();Person two = new Person();}
}

"C:\Program Files\Java\jdk-14.0.1\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\lib\idea_rt.jar=5407:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\Jinfanglin\IdeaProjects\javaSe\out\production\javaSe api_demo.staticCode
静态代码块Process finished with exit code 0