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从头认识java-4.7构造器初始化（2）这一章节我们接着上一章节的内容。（3）静态数据的初始化a.静态数据只会执行一次[java]viewplaincopy1.packagecom.ray.testobject;2.3.publicclassTest{4.privatestaticBookbook1=newBook(1);5.privatestaticBookbook2=newBook(2);6.7.publicTest(){8.System.out.println(createtest);9.book1.say();10.book2.say();11.Bookbook3=newBook(3);12.book3.say();13.}14.15.publicstaticvoidmain(String[]args){16.newTest();17.newTest();18.}19.}20.21.classBook{22.privateintid;23.24.publicBook(intid){25.this.id=id;26.System.out.println(createbook:+id);27.}28.29.publicvoidsay(){30.System.out.println(hi,mynameisbook-+id);31.}32.}输出：createbook:1createbook:2createtesthi,mynameisbook-1hi,mynameisbook-2createbook:3hi,mynameisbook-3createtesthi,mynameisbook-1hi,mynameisbook-2createbook:3hi,mynameisbook-3从结果可以看见，book1和book2只在第一次创建Test的时候创建了一次，然后再次创建Test时就不再创建book1和book2。b.如果不被引用或者不new，对象里面的静态属性域不会创建。我们修改一下上面的代码：[java]viewplaincopy1.packagecom.ray.testobject;2.3.publicclassTest{4.5.publicTest(){6.}7.8.publicstaticvoidmain(String[]args){9.}10.}11.12.classBook{13.privateintid;14.15.publicBook(intid){16.this.id=id;17.System.out.println(createbook:+id);18.}19.20.publicvoidsay(){21.System.out.println(hi,mynameisbook-+id);22.}23.}24.25.classGroupOfBooks{26.privatestaticBookbook;27.28.publicstaticBookgetBook(){29.book=newBook(99);30.returnbook;31.}32.}上面的代码是不会执行newBook(99)这一行的。我们再进行修改，给出两种执行newBook(99)的例子：[java]viewplaincopy1.packagecom.ray.testobject;2.3.publicclassTest{4.5.publicTest(){6.}7.8.publicstaticvoidmain(String[]args){9.newGroupOfBooks().getBook();10.}11.}12.13.classBook{14.privateintid;15.16.publicBook(intid){17.this.id=id;18.System.out.println(createbook:+id);19.}20.21.publicvoidsay(){22.System.out.println(hi,mynameisbook-+id);23.}24.}25.26.classGroupOfBooks{27.privatestaticBookbook;28.29.publicstaticBookgetBook(){30.book=newBook(99);31.returnbook;32.}33.}[java]viewplaincopy1.packagecom.ray.testobject;2.3.publicclassTest{4.5.publicTest(){6.}7.8.publicstaticvoidmain(String[]args){9.GroupOfBooks.getBook();10.}11.}12.13.classBook{14.privateintid;15.16.publicBook(intid){17.this.id=id;18.System.out.println(createbook:+id);19.}20.21.publicvoidsay(){22.System.out.println(hi,mynameisbook-+id);23.}24.}25.26.classGroupOfBooks{27.privatestaticBookbook;28.29.publicstaticBookgetBook(){30.book=newBook(99);31.returnbook;32.}33.}上面两段代码同样输出：createbook:99这里总结一下对象创建的过程：1.查询.class文件的路径2.载入.class文件，执行对象的静态方法或者静态属性域3.new对象，然后分配内存空间（内存空间清零，则对象回收，引用变成null）4.执行属性域初始化5.执行构造器总结：这一章节主要讨论了静态属性域的初始化。这一章节就到这里，谢谢。-----------------------------------目录