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In Java, the plus sign can be used to perform arithmetic addition. It can also be used to concatenate strings. When the plus sign is used inthe manner shown above , the operand on the right is automatically converted to a character string before being concatenated with the operand on the left.
The cast operator is used in this case to purposely convert the integer value contained in the int variable ch2 to a character type suitable for concatenating with the string on the left of the plus sign. Otherwise, Java would attempt toconvert and display the value of the int variable as a series of digits representing the numeric value of the character because the character is stored in a variable of type int .
The increment operator
An extremely important unary operator is the increment operator identified by two plus characters with no space between them (++) .
The increment operator causes the value of its operand to be increased by one.
There is also a decrement operator (--) that causes the value of its operand to be decreased by one.
The increment and decrement operators are used in both prefix and postfix notation.
Prefix and postfix increment and decrement operators
With the prefix version, the operand appears to the right of the operator ( ++X) , while with the postfix version, the operand appears to the left of the operator (X++) .
What's the difference in prefix and postfix?
The difference in prefix and postfix has to do with the point in the sequence of operations thatthe increment (or decrement) actually occurs if the operator and its operand appear as part of a larger overall expression.
(There is effectively no difference if the operator and its operand do not appear as part of a larger overall expression.)
Prefix behavior
With the prefix version, the variable is incremented (or decremented) before it is used to evaluate the larger overall expression.
Postfix behavior
With the postfix version, the variable is used to evaluate the larger overall expression before it is incremented (or decremented) .
Illustration of prefix and postfix behavior
The use of both the prefix and postfix versions of the increment operator is illustrated in the Java program shown in Listing 1 . The output produced by the program is show in the comments at the beginning of the program.
| Listing 1 . Illustration of prefix and postfix notation. |
|---|
/*File incr01.java Copyright 1997, n
Illustrates the use of the prefix and the postfix incrementoperator.
The output from the program follows:a = 5
b = 5a + b++ = 10
b = 6c = 5
d = 5c + ++d = 11
d = 6*********************************************************/
class incr01 { //define the controlling classpublic static void main(String[] args){ //main methodint a = 5, b = 5, c = 5, d = 5;
System.out.println("a = " + a );System.out.println("b = " + b );
System.out.println("a + b++ = " + (a + b++) );System.out.println("b = " + b );
System.out.println();System.out.println("c = " + c );
System.out.println("d = " + d );System.out.println("c + ++d = " + (c + ++d) );
System.out.println("d = " + d );}//end main
}//End incr01 class. |
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