Operators in Java

Maker QR Code ISO/IEC18004 in Java Operators

TABLE 4-1

Highest () ++ * + >> > == & ^ | && || : = Lowest op= [] / >>> >= != << < <= ~ % !

However, if you want to first shift a right by b positions and then add 3 to that result, you will need to parenthesize the expression like this:

In addition to altering the normal precedence of an operator, parentheses can sometimes be used to help clarify the meaning of an expression For anyone reading your code, a complicated expression can be difficult to understand Adding redundant but clarifying parentheses to complex expressions can help prevent confusion later For example, which of the following expressions is easier to read

a | 4 + c >> b & 7 (a | (((4 + c) >> b) & 7))

One other point: parentheses (redundant or not) do not degrade the performance of your program Therefore, adding parentheses to reduce ambiguity does not negatively affect your program

programming language uses control statements to cause the flow of execution to advance and branch based on changes to the state of a program Java s program control statements can be put into the following categories: selection, iteration, and jump Selection statements allow your program to choose different paths of execution based upon the outcome of an expression or the state of a variable Iteration statements enable program execution to repeat one or more statements (that is, iteration statements form loops) Jump statements allow your program to execute in a nonlinear fashion All of Java s control statements are examined here

Java supports two selection statements: if and switch These statements allow you to control the flow of your program s execution based upon conditions known only during run time You will be pleasantly surprised by the power and flexibility contained in these two statements

The if statement was introduced in 2 It is examined in detail here The if statement is Java s conditional branch statement It can be used to route program execution through two different paths Here is the general form of the if statement: if (condition) statement1; else statement2; Here, each statement may be a single statement or a compound statement enclosed in curly braces (that is, a block) The condition is any expression that returns a boolean value The else clause is optional The if works like this: If the condition is true, then statement1 is executed Otherwise, statement2 (if it exists) is executed In no case will both statements be executed For example, consider the following:

int a, b; // if(a < b) a = 0; else b = 0;

Part I:

Here, if a is less than b, then a is set to zero Otherwise, b is set to zero In no case are they both set to zero Most often, the expression used to control the if will involve the relational operators However, this is not technically necessary It is possible to control the if using a single boolean variable, as shown in this code fragment:

boolean dataAvailable; // if (dataAvailable) ProcessData(); else waitForMoreData();

Remember, only one statement can appear directly after the if or the else If you want to include more statements, you ll need to create a block, as in this fragment:

int bytesAvailable; // if (bytesAvailable > 0) { ProcessData(); bytesAvailable -= n; } else waitForMoreData();

Here, both statements within the if block will execute if bytesAvailable is greater than zero Some programmers find it convenient to include the curly braces when using the if, even when there is only one statement in each clause This makes it easy to add another statement at a later date, and you don t have to worry about forgetting the braces In fact, forgetting to define a block when one is needed is a common cause of errors For example, consider the following code fragment:

int bytesAvailable; // if (bytesAvailable > 0) { ProcessData(); bytesAvailable -= n; } else waitForMoreData(); bytesAvailable = n;

It seems clear that the statement bytesAvailable = n; was intended to be executed inside the else clause, because of the indentation level However, as you recall, whitespace is insignificant to Java, and there is no way for the compiler to know what was intended This code will compile without complaint, but it will behave incorrectly when run The preceding example is fixed in the code that follows:

int bytesAvailable; //

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