标识符和美元标识符是由字母、数字和下划线厂符号（$）构成的字符序列标识符必须以字母、下划线或美元符号（$）开头，不能以数字开头一标识符不能是保留字。（参见附录A“Java关键字中关于保留字的列表）。标识符不能是true、false或null。标识符可以为任意长度Liang,IntroductiontoJava Programming,EighthEdition,(c)2011PearsonEducation,Inc.All烟rightsreserved.0132130807
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807 11 标识符 标识符是由字母、数字和下划线（_）和美元 符号（$）构成的字符序列。 标识符必须以字母、下划线（_）或美元符号 （$）开头，不能以数字开头。 – 标识符不能是保留字。(参见附录A “Java关键字 ”中关于保留字的列表）。 标识符不能是 true、false或null。 标识符可以为任意长度
变量// Compute the firstarearadius = l.0;area = radius * radius * 3.14l59;二System.out.println("The area is+area + " for radius"+radius);// Compute the secondarearadius = 2.0;area = radius * radius* 3.14159;1isSystem.out.println("The areaarea + " for radius "+radius);Liang,Introduction to Java Programming,EighthEdition,(c)2011Pearson Education,Inc.All12rightsreserved.0132130807
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807 12 变量 // Compute the first area radius = 1.0; area = radius * radius * 3.14159; System.out.println("The area is “ + area + " for radius "+radius); // Compute the second area radius = 2.0; area = radius * radius * 3.14159; System.out.println("The area is “ + area + " for radius "+radius);
声明变量int x;Declare x to beaninteger variable;Declare radius todoubleradius;/be a double variable;Declare a to becharaaicharacter variable;Liang,Introduction to Java Programming,EighthEdition,(c)2011Pearson Education,Inc.All13rights reserved.0132130807
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807 13 声明变量 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;
赋值语句 Assign 1 to x;X=工1.0;radius三Assign l.o to radius;AAssign 'A' to=aa;Liang,Introduction toJavaProgramming,EighthEdition,(c)2011PearsonEducation,Inc.All14rightsreserved.0132130807
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807 14 赋值语句 x = 1; // Assign 1 to x; radius = 1.0; // Assign 1.0 to radius; a = 'A'; // Assign 'A' to a;
一步完成声明和初始化int x = 1;double d = 1.4;Liang,Introduction to Java Programming,EighthEdition,(c)2011Pearson Education,Inc.All15rightsreserved.0132130807
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807 15 一步完成声明和初始化 int x = 1; double d = 1.4;