Java在它開始運行之前並非被完全加載,其各個部分僅在必需時才加載。
import java.awt.Color;import smallbird.Tools;
public class Parent {
public static final String RG_CODE="025";
public static String CITY_NAME="南京";
public static Color COLOR_RED=new Color(255,0,0);
public static final Object obj=new Child();
static {
System.out.println("static code block."+Tools.getNowDate());
}
public Parent() {
System.out.println("Parent's Constructor."+Tools.getNowDate());
}
public void speak() {
System.out.println("Parent's speak.");
}
}
1、建議將一些常量聲明爲final static編譯期常量。
若僅聲明爲static,打印Parent.CITY_NAME時會先執行靜態代碼塊,而打印Parent.RG_CODE卻不會。
public static final Color COLOR_RED=new Color(255,0,0); 引用類似這些非常數靜態域時會執行static代碼塊,
2、使用.class來獲得對類的引用不會初始化
3、先初始化靜態屬性,再執行靜態代碼塊
System.out.println("test: "+new Parent());
執行結果:
Parent's Constructor.2015-06-29 22:06:55,577
Child's Constructor.
static code block.2015-06-29 22:06:55,578
Parent's Constructor.2015-06-29 22:06:55,578
test: basic.Parent@ae94e92