Introduction to Java Chapter 2 Basic Elements of

Introduction to Java Chapter 2 Basic Elements of Java Chapter 2 - Basic Elements of Java 1

Introduction to Java Names • Java names may contain any number of letters, numbers and underscore (“_”) characters, but they must begin with a letter • Standard Java Naming Convention: – Names beginning with lowercase letters are variables or methods – Names beginning with uppercase letters are class names – Successive words within a name are capitalized – Names in all capital letters are constants Chapter 2 - Basic Elements of Java 2

Introduction to Java Examples of Java Names Legal names: my. Data x 1 Another. Name TWO_PI Illegal names: _to. Upper 1 Day Variable or method names Class names Constant Illegal names Chapter 2 - Basic Elements of Java 3

Introduction to Java Primitive Data Types • Integer data types – byte – short – int – long 8 bits 16 bits 32 bits 64 bits • Real data types - values with a decimal point – float – double 32 bits 64 bits • Other data types – boolean – char 1 bit - true or false 16 bits - Unicode character Chapter 2 - Basic Elements of Java 4

Introduction to Java Strings • Strings are special objects containing one or more characters • String constants are surrounded by double quotes (") Example: "This is a String" • A double quote within a string is represented by the escape sequence ": Example: "She said, "Hello!". " Chapter 2 - Basic Elements of Java 5

Introduction to Java Strings (2) • A plus sign (+) between two strings concatenates them together Example: "This " + "is" produces "This is" • A plus sign (+) between a string and a numeric value converts the numeric value to a string and concatenates the two strings together: int j = 17; "Value = " + j produces the string "Value Chapter 2 - Basic Elements of Java = 17" 6

Introduction to Java Arithmetic Operations • The standard arithmetic operations in Java are: – – – Addition (+) Subtraction (-) Multiplication (*) Division (/) Modulus or Remainder (%) • All of these operations apply to all numeric data types Chapter 2 - Basic Elements of Java 7

Introduction to Java Integer Arithmetic • Arithmetic operations between integers produce integer results by truncating the answer — fractional parts are discarded • Examples: 3 / 4 = 0 4 / 4 = 1 5 / 4 = 1 • Integer arithmetic is unsuitable for calculations involving real-world continuous quantities Chapter 2 - Basic Elements of Java 8

Introduction to Java Real (Floating-Point) Arithmetic • Floating-point arithmetic is used with float and double values. It produces the expected results: 4 / 3 = 1. 3333333 • However, these numbers have range and precision limits: Type float double Range ± 1038 ± 10308 Precision 6 -7 decimal digits 15 -16 decimal digits Chapter 2 - Basic Elements of Java 9

Introduction to Java Assignment Statements • An assignment statement in Java has the form variable. Name = expression; • The expression is evaluated, and the result of the expression is stored in the specified variable. • Assignment statements and arithmetic operations can be combined in a single symbol. For example, variable. Name += expression; is equivalent to variable. Name = variable. Name + expression; – Chapter 2 - Basic Elements of Java 10

Introduction to Java Assignment Conversion • When a value of one type is assigned to a variable of another type, a type conversion must occur • If the new data type can represent a wider range of numbers than the old data type, this is a widening conversion. Widening conversions are legal. • If the new data type can represent a lesser range of numbers than the old data type, this is a narrowing conversion. Narrowing conversions are illegal, and produce compilation errors. Chapter 2 - Basic Elements of Java 11

Introduction to Java Assignment Conversion (2) • Examples: int i = -17; double d; d = i; // Widening conversion int i; double d = -17. 0; i = d; // Narrowing conversion • The first example is legal, while the second one will produce a compile-time error. Chapter 2 - Basic Elements of Java 12

Introduction to Java Casting Conversion • Narrowing conversions are legal if a programmer explicitly specifies them. This is done using the cast operator, which is the name of the new data type in parentheses. Cast operations assign the nearest equivalent value in the new data type. • Examples: byte b; double d = 100000. 0; b = (byte) d; //Legal: result = 127 Chapter 2 - Basic Elements of Java 13

Introduction to Java Increment and Decrement Operators • The increment (++) and decrement (--) operators increase or decrease an integer value by 1. • Preincrement and predecrement operators appear before a variable. They increment or decrement the value of the variable before it is used in the expression. • Example: int i = 4, j = 2, k; k = ++i - j; // i = 5, j = 2, k = 3 Chapter 2 - Basic Elements of Java 14

Introduction to Java Increment and Decrement Operators (2) • Postincrement and postdecrement operators appear after a variable. They increment or decrement the value of the variable after it is used in the expression. • Example: int i = 4, j = 2, k; k = i++ - j; // i = 5, j = 2, k = 2 • Keep expressions involving increment and decrement operators simple! Chapter 2 - Basic Elements of Java 15

Introduction to Java Mathematical Methods • Java’s standard mathematical methods are found in the Math class. They are invoked by naming the class name followed by the method name, separated by a period. For example, the sine of a value can be calculated as: y = Math. sin(x); • A list of standard mathematical methods is found in Table 2 -7. Chapter 2 - Basic Elements of Java 16

Introduction to Java Standard Input and Output • Every Java program has three standard data streams: standard input, standard output, and standard error. Each is represented by an object in the System class. – System. in represents the standard input stream (the keyboard) – System. out represents the standard output stream (the screen) – System. err represents the standard error stream (a special channel to report severe errors on) Chapter 2 - Basic Elements of Java 17

Introduction to Java Standard Input and Output (2) • These objects process input or output data one byte at a time. It is the responsibility of the programmer to combine successive bytes into a useful form, such as a number or a string. • This process is very complex for the standard input stream, and it will not be addressed until Chapter 14. • For now, we will use the convenience class chapman. io. Std. In to read data from the keyboard. Chapter 2 - Basic Elements of Java 18

Introduction to Java Using Class Std. In • First, import package chapman. io • Then create a Std. In object: Std. In in = new Std. In(); • Finally, read values from the standard input stream using methods read. Int(), read. Double(), read. Boolean(), read. String(), etc. Chapter 2 - Basic Elements of Java 19

Introduction to Java Standard Output • Writing to the standard output stream is accomplished with the print() and println() methods. • The difference between these methods is that println() prints the data and advances the cursor to a new one, while print() prints the data and leaves the cursor on the same line Chapter 2 - Basic Elements of Java 20

Introduction to Java Using Input and Output Import class Create Std. In object Write values to output stream with print() and println() methods Read values with Std. In methods Chapter 2 - Basic Elements of Java 21