标识符关键字数据类型（下）

1、变量和它的作用范围,在Java中，每个变量都有类型 在使用变量之前，必须先声明变量的类型。类型可以是简单类型，也可以是引用类型 变量总是在一个类中声明。但一个变量可能和整个类相关联，也可能只在方法体中或某个程序块中起作用,标识符、关键字、数据类型（下）,成员变量/局部变量 值传递 Java编码规范,变量声明的例子（局部变量）,public class test public void aMethod(int j) int m,n,k; String a = “aaaa”,b = “bbbb”; m = j; k = 100; System.out.println(m); System.out.

2、println(n);/Error System.out.println(k); ,变量声明的例子（全局变量）（案例3-6）,public class test int i = 10,p=20; float f,j; f = 100.0f String s1,s2; ,变量的初始化,局部变量在使用之前，必须先初始化。 全局变量如果没有初始化就拿来使用，系统将会自动给它一个默认的初值。,全局变量的默认初值（案例3-7）,传值（案例3-8/3-9）,Java在参数传递时，只使用值传递 当对象实例作为参数传递给方法时，这个参数的值是对象的引用，而不是对象本身,0 x1a4afb,“Lisa”,“ma

3、le”,1,name,sex,grade,18,age,s1,0 x1a4afb,s2,0 x1a4afb,s2=s1,实 例（1）,定义如下类：,class BirthDate private int day; private int month; private int year; public BirthDate(int d, int m, int y) day = d; month = m; year = y; public void setDay(int d) day = d; public void setMonth(int m) month = m; public void se

4、tYear(int y) year = y; public int getDay() return day; public int getMonth() return month; public int getYear() return year; public void display() System.out.println (day + - + month + - + year); ,实 例（2）,运行如下程序：,public class Test public static void main(String args) Test test = new Test(); int date

5、= 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.change2(d1); test.change3(d2); System.out.println(date= + date); d1.display(); d2.display(); public void change1(int i)i = 1234; public void change2(BirthDate b) b = new BirthDate(22,2,2004);

6、public void change3(BirthDate b) b.setDay(22); ,调用过程演示（1）,堆内存,110925,9,587934,354752,Test test = new Test(); int date = 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.change2(d1); test.change3(d2); public void change1(int i) i = 1234; public

7、 void change2(BirthDate b) b = new BirthDate(22,2,2004); public void change3(BirthDate b) b.setDay(22);,test,date,d1,d2,main,栈内存,9,调用过程演示（2）,堆内存,110925,9,587934,test,date,d1,354752,d2,Test test = new Test(); int date = 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000);

8、test.change1(date); test.change2(d1); test.change3(d2); public void change1(int i) i = 1234; public void change2(BirthDate b) b = new BirthDate(22,2,2004); public void change3(BirthDate b) b.setDay(22);,main,change1,i,栈内存,调用过程演示（3）,1234,堆内存,110925,9,587934,test,date,d1,354752,d2,Test test = new Test

9、(); int date = 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.change2(d1); test.change3(d2); public void change1(int i) i = 1234; public void change2(BirthDate b) b = new BirthDate(22,2,2004); public void change3(BirthDate b) b.setDay(22);,m

10、ain,change1,i,栈内存,调用过程演示（4）,堆内存,110925,9,587934,354752,Test test = new Test(); int date = 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.change2(d1); test.change3(d2); public void change1(int i) i = 1234; public void change2(BirthDate b) b =

11、 new BirthDate(22,2,2004); public void change3(BirthDate b) b.setDay(22);,test,date,d1,d2,main,栈内存,调用过程演示（5）,587934,堆内存,110925,9,587934,test,date,d1,354752,d2,Test test = new Test(); int date = 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.

12、change2(d1); test.change3(d2); public void change1(int i) i = 1234; public void change2(BirthDate b) b = new BirthDate(22,2,2004); public void change3(BirthDate b) b.setDay(22);,main,change2,b,栈内存,调用过程演示（6）,587934,堆内存,110925,9,587934,test,date,d1,354752,d2,Test test = new Test(); int date = 9; Birth

13、Date d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.change2(d1); test.change3(d2); public void change1(int i) i = 1234; public void change2(BirthDate b) b = new BirthDate(22,2,2004); public void change3(BirthDate b) b.setDay(22);,main,change2,b,栈内存,调用过程演

14、示（7）,堆内存,110925,9,587934,354752,Test test = new Test(); int date = 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.change2(d1); test.change3(d2); public void change1(int i) i = 1234; public void change2(BirthDate b) b = new BirthDate(22,2,200

15、4); public void change3(BirthDate b) b.setDay(22);,test,date,d1,d2,main,栈内存,调用过程演示（8）,354752,堆内存,110925,9,587934,test,date,d1,354752,d2,Test test = new Test(); int date = 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.change2(d1); test.chang

16、e3(d2); public void change1(int i) i = 1234; public void change2(BirthDate b) b = new BirthDate(22,2,2004); public void change3(BirthDate b) b.setDay(22);,main,b,change3,栈内存,调用过程演示（9）,354752,堆内存,110925,9,587934,test,date,d1,354752,d2,Test test = new Test(); int date = 9; BirthDate d1= new BirthDate(

17、7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.change2(d1); test.change3(d2); public void change1(int i) i = 1234; public void change2(BirthDate b) b = new BirthDate(22,2,2004); public void change3(BirthDate b) b.setDay(22);,main,b,change3,栈内存,调用过程演示（10）,堆内存,110925,9,5879

18、34,354752,Test test = new Test(); int date = 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000); test.change1(date); test.change2(d1); test.change3(d2); public void change1(int i) i = 1234; public void change2(BirthDate b) b = new BirthDate(22,2,2004); public void change3(BirthDate b) b.setDay(22);,test,date,d1,d2,main,栈内存,传值（案例3-10）,再来看一个简单类型数据传值的例子 思考：打印出来的结果是什么？为什么？,Java编程风格,在编写Java程序时，对于类名、变量名、包名、方法名等有一些约定俗成的写法，这种写