Conditionals are where a section of code is only run if certain conditions are met. The most common conditional is the 'if' statement.
The relational operators you've learned so far:
<, <=, >, >=, !=, ==
are sufficient when you only need to check one condition. However what if a particular action is to be taken only if several conditions are true? You can use a sequence of if statements to test the conditions, as follows:
This, however, is hard to write and harder to read. It only gets worse as you add more conditions. Fortunately, Java provides an easy way to handle multiple conditions: the logic operators. There are three logic operators, &&, || and !.
&& is logical and. && combines two boolean values and returns a boolean which is true if and only if both of its operands are true. For instance
boolean b; b = 3 > 2 && 5 < 7; // b is true b = 2 > 3 && 5 < 7; // b is now false
|is logical or.||combines two boolean variables or expressions and returns a result that is true if either or both of its operands are true. For instance|
boolean b; b = 3 > 2 || 5 < 7; // b is true b = 2 > 3 || 5 < 7; // b is still true b = 2 > 3 || 5 > 7; // now b is false
The last logic operator is ! which means not. It reverses the value of a boolean expression. Thus if b is true !b is false. If b is false !b is true.
boolean b; b = !(3 > 2); // b is false b = !(2 > 3); // b is true
These operators allow you to test multiple conditions more easily. For instance the previous example can now be written as