• They should be included to explain the purpose of the program and describe processing steps • They do not affect how a program works • Java comments can take three forms: // this comment runs to the end of the line /* this comment runs to the terminating symbol, even across line breaks */ /** this is a javadoc comment several lines */
public class MyProgram { } public static void main (String[] args) { } /** * comments about the class * */ !"#$%&' (%&) /** * comments about the class */
public class MyProgram { //comments } // comments about the class *+,--'(%&) // Comments everywhere public static void main (String[] args) { } // here also // Comments could be here too
Types The difference between the various numeric primitive types is their size, and therefore the values they can store: Type Size Min Value Max Value byte 8 bits -128 127 short 16 bits -32,768 32,767 int 32 bits -2^31 2^31 - 1 long 64 bits -2^63 2^63 - 1 float 32 bits +/- 3.4 x 1038 with 7 significant digits double 64 bits +/- 1.7 x 10308 with 15 significant digits
class global variables methods statements local variables instructions expressions arithmetic expression relational expression logical expression An expression is a combination of one or more operands and their operators
• Arithmetic expressions compute numeric results and make use of the arithmetic operators: o Addition + o Subtraction – o Minus Unary – o Multiplication * o Division / o Remainder %
Division and Remainder • Dividend / Divisor = Quotient and Remainder • Dividend = (Divisor x Quotient) + Remainder • If both operands to the division operator (/) are integers, the result is an integer (the fractional part is discarded) 14 / 3 equals 4 14 % 3 equals 2 8 / 12 equals 0 8 % 12 equals 8
Precedence • Operators have a well-defined precedence which determines the order in which they are evaluated • Multiplication, division, and remainder are evaluated prior to addition, subtraction, and string concatenation • Arithmetic operators with the same precedence are evaluated from left to right • Parentheses can be used to force the evaluation order
Concatenation • The plus operator (+) is used to concatenate (append) strings: “Hello” + “ World” • To break a string into two parts in two lines, we need to close with a double quote and use + sign to concatenate (append): System.out.println(“ASU is “ + “in Arizona”);
operator • If two operands of + are numbers, it performs an arithmetic addition. • If at least one of operands of + is a string, it performs a string concatenation. • Examples: o 2 + 3 will be 5 o 2 + “ apples” will be “2 apples” o “number ” + 5 will be “number 5” o “we have “ + 2 + 3 will be “we have 23” o “we have “ + (2 + 3) will be “we have 5”
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