基本数据类型和操作.ppt

1、第 2 章 基本数据类型和操作,JDK、JRE与JVM的作用与关系？,JDK: Java Development Kit Java开发工具包， 其中包含Java编译器(javac.exe)、Java运行时环境 JRE：Java Runtime Environment Java运行时环境(Java 虚拟机)+支持类库 JVM：Java Virtual Machine 负责将Java字节码翻译为本地机器可以执行二进制机器码,问题,问题,JDK、JRE与JVM的作用与关系？,学习目标,编写简单的Java程序 (2.2). 使用标识符命名变量、常量、方法和类 (2.3). Java数据类型 使用Jav

2、a运算符书写表达式 (2.7 2.10). 使用 JOptionPane 输入对话框输入 (2.14). 熟悉Java的文档管理、编程风格和命名习惯 (2.18).,编写一个简单的程序,计算的圆的面积.,ComputeArea,Run,跟踪程序执行过程,public class ComputeArea /* Main method */ public static void main(String args) double radius; double area; / Assign a radius radius = 20; / Compute area area = radius * rad

3、ius * 3.14159; / Display results System.out.println(The area for the circle of radius + radius + is + area); ,no value,radius,为 radius分配内存单元,跟踪程序执行过程,public class ComputeArea /* Main method */ public static void main(String args) double radius; double area; / Assign a radius radius = 20; / Compute a

4、rea area = radius * radius * 3.14159; / Display results System.out.println(The area for the circle of radius + radius + is + area); ,no value,radius,memory,no value,area,为 area分配内存单元,跟踪程序执行过程,public class ComputeArea /* Main method */ public static void main(String args) double radius; double area;

5、/ Assign a radius radius = 20; / Compute area area = radius * radius * 3.14159; / Display results System.out.println(The area for the circle of radius + radius + is + area); ,20,radius,no value,area,assign 20 to radius,跟踪程序执行过程,public class ComputeArea /* Main method */ public static void main(Strin

6、g args) double radius; double area; / Assign a radius radius = 20; / Compute area area = radius * radius * 3.14159; / Display results System.out.println(The area for the circle of radius + radius + is + area); ,20,radius,memory,1256.636,area,compute area and assign it to variable area,跟踪程序执行过程,publi

7、c class ComputeArea /* Main method */ public static void main(String args) double radius; double area; / Assign a radius radius = 20; / Compute area area = radius * radius * 3.14159; / Display results System.out.println(The area for the circle of radius + radius + is + area); ,20,radius,memory,1256.

8、636,area,控制台输出信息,数据类型,I）值类型(Value Type)、基本类型、原生类型 8种,II）引用类型(Reference Type)、类类型 很多,值类型,引用类型(Reference Type),java.lang.Byte java.lang.Short java.lang.Integer: int值类型的包装类 java.lang.Long：long值类型的包装类 java.lang.Float java.lang.Double java.lang.Character java.lang.Boolean java.lang.String,变量,值类型名 变量名 = 值

9、; 引用类型名 变量名 = new 构造方法();,变量名可以包含中文吗？,标识符,标识符是一个由字母、数字、下划线(_)和美元符号($)构成的字符转. 标识符必须由字母、下划线(_)或美元符号开始，不能用数字开头。 标识符不能是保留字（参见附录A）。 标识符不能是 true, false和null. 标识符可以有任何长度.,变量,/ Compute the first area radius = 1.0; area = radius * radius * 3.14159; System.out.println(The area is “ + area + for radius +radius

10、); / Compute the second area radius = 2.0; area = radius * radius * 3.14159; System.out.println(The area is “ + area + for radius +radius);,变量说明,int x; / Declare x to be an / integer variable; double radius; / Declare radius to / be a double variable; char a; / Declare a to be a / character variable

11、;,变量名使用小写字母，如果一个名字有多个词组成，每个词的第一个字母大写,赋值语句,x = 1; / Assign 1 to x; radius = 1.0; / Assign 1.0 to radius; a = A; / Assign A to a;,在第一步中说明和初始化变量,int x = 1; double d = 1.4; float f = 1.4;,Is this statement correct?,float f = 1.4f,常量,final datatype CONSTANTNAME = VALUE; final double PI = 3.14159; final i

12、nt SIZE = 3;,常量用大写字母命名，例如PI,算术运算符,+, -, *, /, and % 5 / 2结果为整型2. 5.0 / 2结果为double类型2.5 5 % 2 结果为 1 (求余数),January 1, 2005 是 Saturday, 可推算 February 1, 2005 是 Tuesday,注意,浮点型数不一定是精确存储. 例如, System.out.println(1 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1); 显示 0.5000000000000001, 而不是 0.5, System.out.println(1.0 - 0.9);

13、 显示 0.09999999999999998, 而不是 0.1. 整型数据是精确存储.,数值直接量,直接量是在程序中直接出现的常量值。 int i = 34; 整型直接量在 -231 (-2147483648) 到 2311 (2147483647) 之间.long类型在其后加L. 浮点型默认为 double 类型. float类型在其后加f 或F, double 类型加 d or D. 例如： float ：100.2f or 100.2F, double ：100.2d or 100.2D. 科学计数法可表示为： 1.23456e+2, 或者 1.23456e2, 等价于 123.456

14、, and 1.23456e-2 等价于 0.0123456.,算术表达式,翻译成 (3+4*x)/5 10*(y-5)*(a+b+c)/x + 9*(4/x + (9+x)/y),简捷赋值运算符,OperatorExample等价于 +=i+=8i = i+8 -=f-=8.0f = f-8.0 *=i*=8i = i*8 /=i/=8i = i/8 %=i%=8i = i%8,增量和减量运算符,Operator Name Description +var前置增量运算符 表达式执行前变量var先加1. var+后置增量运算符 表达式执行后变量var加1. -var前置减量运算符 表达式执行前

15、变量var先减1. var-后置减量运算符 表达式执行后变量var减1,赋值表达式和赋值语句,以下表达式可作语句: variable op= expression; / op 可选 +, -, *, /, or % +variable; variable+; -variable; variable-;,数值类型转换,考虑以下语句: byte i = 100; long k = i * 3 + 4; double d = i * 3.1 + k / 2;,Byte, short, int, long, float, double,范围增加,扩宽可自动转换,缩窄需明确指明,类型转换,隐式转换 do

16、uble d = 3; (类型拓宽) 显式转换 int i = (int)3.0; (类型所在) int i = (int)3.9; (小数部分被截去) What is wrong?int x = 5 / 2.0;,字符型数据类型,char letter = A; (ASCII) char numChar = 4; (ASCII) char letter = u0041; (Unicode) char numChar = u0034; (Unicode),4位十六进制组成.,注意：字符型可作自加、自减运算 char ch = a; System.out.println(+ch);,Unicod

17、e 统一码,Unicode 占2个字节, 以 u开头的4个16进制数，范围从u0000 到 uFFFF. 共65536个字符。,Unicode u03b1 u03b2 u03b3 for three Greek letters,特殊字符的转义字符序列,Description Escape Sequence Unicode Backspace bu0008 Tab tu0009 换行 nu000A 回车 ru000D 斜杠 u005C 单引号 u0027 双引号 u0022,字符型和数值型之间的转换,int i = a; / Same as int i = (int)a; char c = 97

18、; / Same as char c = (char)97;,比较运算符,Operator Name greater than =greater than or equal to =equal to !=not equal to,布尔运算符,Operator Name !not 或者能被400整除, (Equality) int x= (a+)+ a; int a = 0; int x = +a + a;,X=1,X=2,表达式计算的规则,规则1：可能的情况下，从左向右依次计算所有的表达式； 规则2：根据运算符的优先级进行运算； 规则3：对优先级相同的相邻运算符，根据结合方向进行运算。,表达式

19、计算的规则, 根据规则，表达式 3 + 4 * 4 5 * (4 + 3) - 1 的计算如下:,String 类型,String实际上Java定义的一个类。 例如：String message = Welcome to Java;,字符串可以用“+”链接起来 / Three strings are concatenated String message = Welcome + to + Java; / String Chapter is concatenated with number 2 String s = Chapter + 2; / s becomes Chapter2 / Stri

20、ng Supplement is concatenated with character B String s1 = Supplement + B; / s becomes SupplementB,字符串转为数值,int intValue = Integer.parseInt(intString); intString 是一个数值型字符串，例如 “123”. double doubleValue =Double.parseDouble(doubleString); doubleString是一个数值型字符串，例如 “123.45”.,String s = String.valueOf( val

21、ue); 其中 value 为任意一种数字类型。,从输入对话框获取输入,String string = JOptionPane.showInputDialog( null, “Prompting Message”, “Dialog Title”, JOptionPane.QUESTION_MESSAGE);,两种调用方法,第一种： String string = JOptionPane.showInputDialog(null, x, y, JOptionPane.QUESTION_MESSAGE); 第一个参数总是null， x 表示显示内容的字符串, y 表示对话框的标题，第四个参数是对话

22、框显示的图标. 第二种： JOptionPane.showMessageDialog(x); x 表示显示内容的字符串,Example 2.3 计算贷款支付额,ComputeLoan,Run,输入年利率、年数和贷款总额 显示月支付额和总支付额,Example 2.4 整钱兑零,输入总钱数，然后兑换成 dollars(1元), quarters(2角5分), dimes(1角), nickels(5分), and pennies(1分).,ComputeChange,Run,程序跟踪,int remainingAmount = (int)(amount * 100); / Find the nu

23、mber of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; / Find the number of quarters in the remaining amount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; / Find the number of dimes in the remaining amount i

24、nt numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; / Find the number of nickels in the remaining amount int numberOfNickels = remainingAmount / 5; remainingAmount = remainingAmount % 5; / Find the number of pennies in the remaining amount int numberOfPennies = remaining

25、Amount;,1156,remainingAmount,remainingAmount initialized,Suppose amount is 11.56,程序跟踪,int remainingAmount = (int)(amount * 100); / Find the number of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; / Find the number of quarters in the remaining am

26、ount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; / Find the number of dimes in the remaining amount int numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; / Find the number of nickels in the remaining amount int numberOfNickels = re

27、mainingAmount / 5; remainingAmount = remainingAmount % 5; / Find the number of pennies in the remaining amount int numberOfPennies = remainingAmount;,1156,remainingAmount,Suppose amount is 11.56,11,numberOfOneDollars,numberOfOneDollars assigned,程序跟踪,int remainingAmount = (int)(amount * 100); / Find

28、the number of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; / Find the number of quarters in the remaining amount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; / Find the number of dimes in the remaining am

29、ount int numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; / Find the number of nickels in the remaining amount int numberOfNickels = remainingAmount / 5; remainingAmount = remainingAmount % 5; / Find the number of pennies in the remaining amount int numberOfPennies = rem

30、ainingAmount;,56,remainingAmount,Suppose amount is 11.56,11,numberOfOneDollars,remainingAmount updated,程序跟踪,int remainingAmount = (int)(amount * 100); / Find the number of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; / Find the number of quarte

31、rs in the remaining amount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; / Find the number of dimes in the remaining amount int numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; / Find the number of nickels in the remaining amount in

32、t numberOfNickels = remainingAmount / 5; remainingAmount = remainingAmount % 5; / Find the number of pennies in the remaining amount int numberOfPennies = remainingAmount;,56,remainingAmount,Suppose amount is 11.56,11,numberOfOneDollars,2,numberOfOneQuarters,numberOfOneQuarters assigned,程序跟踪,int rem

33、ainingAmount = (int)(amount * 100); / Find the number of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; / Find the number of quarters in the remaining amount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; / F

34、ind the number of dimes in the remaining amount int numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; / Find the number of nickels in the remaining amount int numberOfNickels = remainingAmount / 5; remainingAmount = remainingAmount % 5; / Find the number of pennies in the remaining amount int numberOfPennies = remainingAmount;,6,remainingAmount,Suppose amount is 11.56,11,numberOfOneDollars,2,numberOfQuarters,remainingAmount updated,格式化输出,JDK 1.5