TR–Java–lecture04–datatype〔数据类型).ppt

Java程序设计 Java Programming Spring, 2009 Contents (Chapter 6 in Textbook) Data Types(数据类型) Operators(运算符) Expressions(表达式) Arrays(数组) 包装器类 字符串类 名字含义 控制流语句 Data in Java Java is a “typed” language: Every data value must have a type The type gives rules for what values are allowed, and what operations can be done with the values. For the computer, values of a certain type usually take a known amount of storage space in memory Data in Java Primitive types(基本数据类型) A primitive type represents a single value, which cannot be decomposed. Reference types(引用数据类型) The reference types are class types, interface types and array types. Variables of these types can refer to objects of the corresponding type. Primitive Data Type Java has a number of pre-defined primitive data types. boolean Boolean (logical) values, either true or false char single character byte 8-bit integers (signed) short 16-bit integers (signed) int 32-bit integers (signed) (e.g. 3) long 64-bit integers (signed) float 32-bit floating point double 64-bit floating point (e.g. 3.0) The Boolean Type A Boolean variable is one which can have only 2 possible values: true or false. Boolean variables are used when you need to do logical tests Example: “Is X greater than 3?” x 3 Type int A variable of type int may take values from–2147483648 to 2147483647. Exceeding the range of legal values results in OVERFLOW, a run-time error. Base of the number: octal(8进制)— a leading 0(zero) hexadecimal(16进制) — a leading 0x or 0X decimal(10进制) Type long（长整数） A variable of type long may take values from–9223372036854775808L to 9223372036854775807L. To indicate the difference between an int constant and a long constant, the character L/l is appended. Example 2 is of type int 2L is of type long Type float（长整数） float :4个字节，32位 从1.40129846432481707e-45到 3.40282346638528860e+38 (正值或负值的绝对值) 数字后必须用f指明，否则属于double型。 Type double (Literals，直接量) Type double represents “real” numbers approximately from -1.7 ? 10308 to 1.7 ? 1