Loops and Logic - Beginning Java - page 95

Logical AND Operations
You can use either of the AND operators, && or & , where you have two logical expressions that must both be
true for the result to be true — that is, you only want to be rich and healthy. Either AND operator produces
the same result from the logical expression. I come back to how they differ in a moment. First, let's explore
how they are used. All of the following discussion applies equally well to & as well as to && .
Let's see how logical operators can simplify the last example. You could use the && operator if you test
a variable of type char to determine whether it contains an uppercase letter or not. The value being tested
must be both greater than or equal to ' A ' AND less than or equal to ' Z '. Both conditions must be true for
the value to be a capital letter. Taking the example from our previous program, with a value stored in a char
variable symbol , you could implement the test for an uppercase letter in a single if by using the && operator:
if(symbol >= 'A' && symbol <= 'Z')
System.out.println("You have the capital letter " + symbol);

If you look at the precedence table in Chapter 2, you see that the relational operators are executed before
the && operator, so no parentheses are necessary. Here, the output statement is executed only if both of the
conditions combined by the operator && are true . However, as I have said before, it is a good idea to add
parentheses if they make the code easier to read. It also helps to avoid mistakes.
In fact, the result of an && operation is very simple. It is true only if both operands are true ; otherwise,
the result is false .
You can now rewrite the set of if s from the last example.

TRY IT OUT: Deciphering Characters the Easy Way
You can replace the outer if - else loop and its contents in LetterCheck.java as shown in the following
code:

public class LetterCheck2 {
public static void main(String[] args) {
char symbol = 'A';
symbol = (char)(128.0*Math.random()); // Generate a random
character
if(symbol >= 'A' && symbol <= 'Z') { // Is it a capital

letter

System.out.println("You have the capital letter " + symbol);
} else {
if(symbol >= 'a' && symbol <= 'z') { // or is it a small

letter?

System.out.println("You have the small letter " + symbol);
} else { // It is not less

than z

System.out.println("The code is not a letter");

}

}