[Java]Java的Static block與建構子(constructor)

Static block是Java中的一個用來初始化Static屬性的功能
一個Class中的Static block只會執行一次
建構子(constructor)則是每次new一個物件的時候就會執行一次

建構子的名稱要與class名稱相同，並且不允許同樣參數的建構子

使用static block與constructor的方法範例如下

public class StaticInitDemo {

 private static String message;

 private String message2;

 

 static{

  System.out.println("static block initialize");

  setMessage("This is an demo of static block");

 }

 

 public StaticInitDemo(){

  System.out.println("constructor initialize");

  setMessage2("This message is generate as constructor");  

 }

 public StaticInitDemo(String str){

  System.out.println("constructor with parameter initialize");

  setMessage2("str="+str);  

 }

 public static String getMessage() {

  return message;

 }

 public static void setMessage(String message) {

  StaticInitDemo.message = message;

 }

 public String getMessage2() {

  return message2;

 }

 public void setMessage2(String message2) {

  this.message2 = message2;

 }

 

}//end of class

public class StaticBlockDemo {



 public static void main(String[] args) {

  System.out.println("Test begin\n");

  

  System.out.println("StaticBlock:");

  System.out.println(StaticInitDemo.getMessage());

  

  System.out.println("\n"+"Constructor:");

  StaticInitDemo demo = new StaticInitDemo();  

  System.out.println(demo.getMessage2());

  StaticInitDemo demo2 = new StaticInitDemo(); 



 }



}//end of class

執行結果為：

Test begin

StaticBlock:

static block initialize

This is an demo of static block

Constructor:

constructor initialize

This message is generate as constructor

constructor initialize