Java第二阶段---11封装---第四节 static 修饰符

1.static 修饰符应用范围

static修饰符只能用来修饰类中定义的成员变量、成员方法、代码块以及内部类(内部类有专门章节进行讲解)。

2.static 修饰成员变量

static 修饰的成员变量称之为类变量。属于该类所有成员共享。

示例

package cn.lyxq.test04;public class ChinesePeople {private String name;private  int age;public static String country = "中国";public ChinesePeople(String name,int age){this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}
}

package cn.lyxq.test04;public class ChinesePeopleTest {public static void main(String[] args) {ChinesePeople cp1 = new ChinesePeople("张三",20);System.out.println(ChinesePeople.country);ChinesePeople.country="日本";ChinesePeople cp2 = new ChinesePeople("李四",30);System.out.println(ChinesePeople.country);ChinesePeople cp3 = new ChinesePeople("王五",32);System.out.println(ChinesePeople.country);}}

如果类变量是公开的，那么可以使用 类名.变量名 直接访问该类变量

3.static 修饰成员方法

static 修饰的成员方法称之为类方法，属于该类所有成员共享。

package cn.lyxq.test04;public class ChinesePeople {private String name;private  int age;private static String country = "中国";public ChinesePeople(String name,int age){this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}//类方法public static String getCountry() {return country;}//类方法public static void setCountry(String country) {ChinesePeople.country = country;}
}

package cn.lyxq.test04;public class ChinesePeopleTest {public static void main(String[] args) {ChinesePeople cp1 = new ChinesePeople("张三",20);ChinesePeople.setCountry("日本");ChinesePeople cp2 = new ChinesePeople("李四",30);System.out.println(ChinesePeople.getCountry());ChinesePeople cp3 = new ChinesePeople("王五",32);System.out.println(cp3.getCountry());//不是最优访问方式}}

如果类方法是公开的，那么可以使用 类名.方法名直接访问该类方法。

4.static 修饰代码块

static 修饰的代码块被称为静态代码块，在JVM第一次记载该类时执行。因此，静态代码代码块只能执行一次，通常用于一些系统设置场景。

package cn.lyxq.test04;public class ChinesePeople {private String name;private  int age;//使用static修饰的成员变量称为类变量，不会随着成员变化而变化，属于所有成员共享private static String country ;//static修饰的代码块称为静态代码块，在JVM第一次加载该类的时候执行，只能执行一次static{country = "中国";System.out.println("country属性已经被赋值");}public ChinesePeople(String name,int age){this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}//类方法public static String getCountry() {return country;}//类方法public static void setCountry(String country) {ChinesePeople.country = country;}
}

package cn.lyxq.test04.test;import  cn.lyxq.test04.ChinesePeople;public class ChinesePeopleTest {public static void main(String[] args) {ChinesePeople cp = new ChinesePeople("张三",20);}}

5.static内存