覺得Core Java在Java 初始化過程的總體順序沒有講,只是說了構(gòu)造器時(shí)的順序,作者似乎認(rèn)為路徑很多,列出來比較混亂.我覺得還是要搞清楚它的過程比較好.所以現(xiàn)在結(jié)合我的學(xué)習(xí)經(jīng)驗(yàn)寫出具體過程:
過程如下:
1.在類的聲明里查看有無靜態(tài)元素(static element, 我姑且這么叫吧),比如static int? x = 1,
{//block
??????float sss = 333.3; String str = "hello";
}
或者 比如
?static {? //(static block),
????????????int x = 2;
????????????double y = 33.3;
}
如果有static element則首先執(zhí)行其中語句,但注意static element只執(zhí)行一次,在第二次創(chuàng)建類的對(duì)象的時(shí)候，就不會(huì)去執(zhí)行static element的語句.
2.查看此類是否為啟動(dòng)運(yùn)行類,若為啟動(dòng)運(yùn)行類,則執(zhí)行main()方法里的語句對(duì)應(yīng)語句
3.若不是啟動(dòng)運(yùn)行類,則按代碼的排版先后順序繼續(xù)執(zhí)行非static element的變量賦值以及代碼塊.
4.最后執(zhí)行構(gòu)造方法,如果在被調(diào)用的構(gòu)造方法里面有this關(guān)鍵字(注意,如果你考慮要調(diào)用其他構(gòu)造方法,則應(yīng)該把this寫在最前面,不然會(huì)產(chǎn)生錯(cuò)誤),則先調(diào)用相應(yīng)構(gòu)造方法主體,調(diào)用完之后再執(zhí)行自己的剩下語句.
下面給出一個(gè)實(shí)例:
/**
?*
?* @author livahu
?* Created on 2006年9月6日, 下午17:00
?*/
class FirstClass {
??? FirstClass(int i) {
??????? System.out.println("FirstClass(" + i + ")");
??? }
???
??? void useMethod(int k) {
??????? System.out.println("useMethod(" + k + ")");
??? }
}
class SecondClass {
??? static FirstClass fc1 = new FirstClass(1);
??? FirstClass fc3 = new FirstClass(3);
??? static {
??????? FirstClass fc2 = new FirstClass(2);
??? }
???
??? {
??????? System.out.println("SecondClass's block, this block is not static block.");
??? }
???
??? SecondClass() {
??????? System.out.println("SecondClass()");
??? }
???
??? FirstClass fc4 = new FirstClass(4);
}
public class InitiationDemo {
??? SecondClass sc1 = new SecondClass();
???
??? {
??????? System.out.println("Hello Java World!");
??? }
???
??? public static void main(String[] args) {
??????? System.out.println("Inside main()");
??????? SecondClass.fc1.useMethod(100);
??????? InitiationDemo idObj = new InitiationDemo();
??? }
???
??? static SecondClass sc2 = new SecondClass();
}
運(yùn)行結(jié)果:
FirstClass(1)
FirstClass(2)
FirstClass(3)
SecondClass's block, this block is not static block.
FirstClass(4)
SecondClass()
Inside main()
useMethod(100)
FirstClass(3)
SecondClass's block, this block is not static block.
FirstClass(4)
SecondClass()
Hello Java World!