java-Static關鍵字

標籤：方法   rri   str   停止   簡單   color   win   開始   interface   

1.使用static關鍵字聲明的屬性為全域屬性

未使用static關鍵字指定city之前，如果需要將Tom,Jack,Mary三人的城市均改成Beijing,需要再次聲明三次對象的city為Beijing

 

 1 package packageone; 2 class People{ 3     String name; 4     String city  = "Shanghai"; 5     public People(String name) { 6         this.name = name; 7     } 8     public void showInfo() { 9         System.out.println("姓名:"+name+","+"城市:"+city);10     }11 }12 public class StaticDemo {13 14     public static void main(String[] args) {15         People p1 = new People("Tom");16         p1.city = "Beijing";17         p1.showInfo();18         People p2 = new People("Jack");19         p2.city = "Beijing";20         p2.showInfo();21         People p3 = new People("Mary");22         //未聲明p3對象的city屬性為Beijing,則其city仍為Shanghai。23         p3.showInfo();24     }25 }

 

使用static關鍵字指定city後，只需設定city = “Beijing”一次,即可實現三個人城市的更改

 1 package packageone; 2 class People{ 3     String name; 4     static String city  = "Shanghai"; 5     public People(String name) { 6         this.name = name; 7     } 8     public void showInfo() { 9         System.out.println("姓名:"+name+","+"城市:"+city);10     }11 }12 public class StaticDemo {13 14     public static void main(String[] args) {15         People p1 = new People("Tom");16         p1.city = "Beijing";17         p1.showInfo();18         People p2 = new People("Jack");19         p2.showInfo();20         People p3 = new People("Mary");21         //未聲明p3對象的city屬性為Beijing,但其city變為Beijing。22         p3.showInfo();23     }24 }

2.使用static關鍵字聲明的屬性和方法可直接通過類名來調用（代碼作為對該static應用的解釋有點複雜了，同時是介面的簡單使用）

 

 1 package packageone; 2  3 interface USB { 4     void start(); 5     void stop(); 6 } 7  8 class C { 9     public static void work(USB u) {10         u.start();11         System.out.println("工作中");12         u.stop();13     }14 }15 16 class USBDisk implements USB {17     @Override18     public void start() {19         System.out.println("隨身碟開始工作");20     }21 22     @Override23     public void stop() {24         System.out.println("隨身碟停止工作");25     }26 }27 28 class Printer implements USB {29     @Override30     public void start() {31         System.out.println("印表機開始工作");32     }33 34     @Override35     public void stop() {36         System.out.println("印表機停止工作");37     }38 }39 40 public class interfacetest {41     public static void main(String[] args) {42         //直接通過類名來調用work方法43         C.work(new USBDisk());44         C.work(new Printer());45     }46 47 }

 

3.注意：】使用static方法的時候，只能訪問static聲明的屬性和方法，而非static聲明的屬性和方法是不能訪問的。而非static聲明的方法是可以去調用static聲明的屬性或方法

 1 package packageone; 2 //由於博主我水平有限參考了別人的代碼案例,但由於他的代碼有較大錯誤，經調試成功後援引，算是自己的代碼了吧~嘿嘿 3 class People { 4     private String name; 5     private int age; 6  7     public String getName() { 8         return name; 9     }10 11     public void setName(String name) {12         this.name = name;13     }14 15     public int getAge() {16         return age;17     }18 19     public void setAge(int age) {20         this.age = age;21     }22 23     // 使用static定義country屬性24     private static String country = "China";25 26     // 定義static方法,修改static屬性27     public static void setCountry(String c) {28         country = c;29     }30 31     // 取得static屬性32     public static String getCountry() {33         return country;34     }35 36     // 通過構造方法為屬性賦值(初始化操作)37     public People(String name, int age) {38         this.name = name;39         this.age = age;40     }41 42     public void info() {43         System.out.println("姓名:"+ getName()+"年齡:"+getAge()+"城市:"+country);44     }45 }46 47 public class StaticDemo {48     public static void main(String args[]) {49         People per1 = new People("張三", 20);50         People per2 = new People("李四", 21);51         People per3 = new People("王五", 23);52         System.out.println("--------- 修改前-----------");53         per1.info();54         per2.info();55         per3.info();56         System.out.println("--------- 修改後-----------");57         // 直接使用類名稱調用方法來修改static屬性的內容,正是因為country為static全域變數,才不需要每個人都去修改國籍58         People.setCountry("USA");59         per1.info();60         per2.info();61         per3.info();62     }63 }

 

java-Static關鍵字