 Java has the logical operators and, or, and not, symbolized by &&, ||, and !, respectively.  Logical or means one or the other or both conditions hold true.  It is also possible to devise logical expressions which have the meaning of exclusive or, which means one or the other, but not both hold true.  Parentheses can be used in logical expressions to clarify the grouping of different conditions.  Once the logical operators are available it becomes possible to construct complex conditions.

 if(condition1)  {  if(condition2)  {  statement1;  }  else  {  statement2;  }  else  {  if(condition3)  {  statement3;  }  else  {  statement4;  }  statement1 is executed if condition1 is true and condition2 is true.  statement2 is executed if condition1 is true and condition2 is not true.  statement3 is executed if condition1 is not true and condition3 is true.  statement4 is executed if condition1 is not true and condition3 is not true.  The combination of conditions for the previous example is repeated here:

 The code given below, using the logical operators, is equivalent to the code given previously, using nested if s:  if(condition1 && condition2)  {  statement1;  }  else if(condition1 && !condition2)  {  statement2;  }  else if(!condition1 && condition3)  {  statement3;  }  else if(!condition1 && !condition3)  {  statement4;  }  else  {  }  statement1 is executed if condition1 is true and condition2 is true.  statement2 is executed if condition1 is true and condition2 is not true.  statement3 is executed if condition1 is not true and condition3 is true.  statement4 is executed if condition1 is not true and condition3 is not true.

 It is the programmer’s choice whether to use nested if s or logical operators.  It is possible to construct arbitrarily complex logical expressions.  Depending on the variables at hand and their meanings, you may have statements involving more than one numerical variable.  They could take the following form:  if(x 12)…

 You may also have comparisons involving a single numerical variable that bring up properties of number lines from algebra. Here are four such examples:  if(x 12) Never true:  A value can never be less than 5 and more than 12 at the same time. The statement after this if statement will never be executed in any case.

 if(x 12)  True for values outside of the range from 5 to 12:  if(x > 5 && x < 12)  True for values inside the range from 5 to 12

 if(x > 5 || x < 12) Always true:

 When using if statements, execution of certain blocks of code depends on the truth value of conditions such as numeric comparisons of equality and inequality.  Depending on the values of variables, each condition has a value of true or false.

 Java has a simple type called boolean that can contain truth values.  true and false are keywords designating the two values a boolean variable can contain.  Here is an example of declaration and assignment:  boolean someResult;  someResult = true;  someResult = false;

 The next question to consider is that of notifying the user when one of several possible actions is taken by a method.  The way to do this is by giving the method a type and a return value that signifies which action was taken.  For a method where there are essentially two alternatives, either some action or no action, a boolean return value is a reasonable choice.

 The increaseSeedCount() method is rewritten below to return a value indicating whether the seedCount was increased or not.  The method is now typed boolean and one of the two boolean values is returned at the end of the two different execution paths through the method.  public boolean increaseSeedCount(int addedNumber)  {  if(addedNumber > 0)  {  seedCount = seedCount + addedNumber;  return true;  }  else  return false;  }

 In code that makes use of the method, a call would take the form illustrated in the following fragment:  boolean callResult;  int moreSeeds = 7;  Cup4 myCup = new Cup4(5);  callResult = myCup.increaseSeedCount(moreSeeds);

 After the call it would be possible to take certain actions in the program depending on whether the return value was true or false.  The structure of such actions might be further if statements.  Note that when using boolean values in if conditions, it is not necessary to use a comparison symbol to test equality.

 It is sufficient to use a variable containing the truth value by itself.  For example, a line of code like that shown below could follow the code shown above.  The variable callResult alone could serve as the contents of an if condition:  if(callResult)  …

 It is also possible to write code in the form shown below.  This is not recommended for beginning programmers because it can be difficult to read.  The call to increase the seedCount is embedded in the parentheses of the if statement.  When the call is made, a truth value is returned.  The action of the if statement depends on this return value, which is unnamed and “invisible”.  if(myCup.increaseSeedCount(moreSeeds))  …

 It is true in general that it is not necessary to capture the return value.  There may be cases where you aren’t interested in the return value.  If so, it can be ignored and this is not a syntactical error.  For example, this is a valid line of code:  myCup.increaseSeedCount(moreSeeds);

 Notice that in the increaseSeedCount() method code there were two return statements.  They were in the two mutually exclusive alternatives of an if statement.  Whenever a return statement is encountered this ends the execution of the method.  It is possible to consolidate such a situation by assigning a return value to a variable and returning the variable at the bottom of the method.

 Here is the method modified in that way:  public boolean increaseSeedCount(int addedNumber)  {  boolean returnValue;   if(addedNumber > 0)  {  seedCount = seedCount + addedNumber;  returnValue = true;  }  else  returnValue = false;   return returnValue;  }

 This code is neither better nor worse than the previous version in an absolute sense.  Conceptually, it does illustrate the fact that you can ultimately only return once out of any method.  Also, this might be useful in the case where you don’t want to return right away.  For instance, you may want to decide to return true or false, then do some other functionality before returning.