java课件lecture2.ppt

2-* Assignment Operators Often we perform an operation on a variable, and then store the result back into that variable Java provides assignment operators to simplify that process For example, the statement num += count; is equivalent to num = num + count; 2-* Assignment Operators There are many assignment operators in Java, including the following: Operator += -= *= /= %= Example x += y x -= y x *= y x /= y x %= y Equivalent To x = x + y x = x - y x = x * y x = x / y x = x % y 2-* Assignment Operators The right hand side of an assignment operator can be a complex expression The entire right-hand expression is evaluated first, then the result is combined with the original variable Therefore result /= (total-MIN) % num; is equivalent to result = result / ((total-MIN) % num); 2-* Outline Character Strings Variables and Assignment Primitive Data Types Expressions Data Conversion 2-* Data Conversion Sometimes it is convenient to convert data from one type to another For example, in a particular situation we may want to treat an integer as a floating point value These conversions do not change the type of a variable or the value thats stored in it – they only convert a value as part of a computation 2-* Data Conversion Conversions must be handled carefully to avoid losing information Widening conversions are safest because they tend to go from a small data type to a larger one (such as a short to an int) Narrowing conversions can lose information because they tend to go from a large data type to a smaller one (such as an int to a short) In Java, data conversions can occur in three ways: assignment conversion promotion casting 2-* Assignment Conversion Assignment conversion occurs when a value of one type is assigned to a variable of another If money is a float variable and dollars is an int variable, the following assignment converts the value in dollars to a float money = dollars Only widening conversions can happen via assignment Note that the value or t