Each operator produces either the value true or the value false, and so is eminently suited to the business of making decisions.
The value of the variable state is set to true in the assignment statement if x - y is less than a + b, and to false otherwise. The first statement you look at that can make use of the result of a comparison is the if statement. If the value of expression is true, the statement that follows the if is executed; otherwise, it isn't. The if condition between the parentheses tests whether the value of number is odd by comparing the remainder that results from dividing it by 2 with 0.
In general, wherever you can have one executable statement in Java, you can also have a block of statements enclosed between braces, {}.
Now if the value of expression is true, all the statements enclosed in the following block are executed; if expression is false, the statements in the block are not executed.
Statement blocks are more than just a convenient way of grouping statements together?they affect the life and accessibility of variables. This provides an explicit choice between two courses of action, one for when the if expression is true and another for when it is false.
The statement that is executed when an if expression is true can be another if, as can the statement in an else clause. With nested ifs, it is often difficult to discern which if statement to which a particular else clause belongs. Note how the logic has substantially changed from the previous version, in spite of the fact that the indentation implies otherwise. You can't compare variables of an enumeration type using the comparison operators but you can compare them using a method that every enumeration object provides.
After defining the variable, best, you test whether the value of season is the same value as best.
Often you will need to combine a number of conditions in order to execute a particular course such as when all conditions are true simultaneously. The AND and OR operators are very simple; the only point of potential confusion is the fact that you have the choice of two operators for each of AND and OR.
The exclusive OR results is true when its operands are different, so when one operand has the value true and the other has the value false, the result is true.
The third type of logical operator, !, applies to one boolean operand, and the result is the inverse of the operand value. Although testing characters using logical operators is a useful way of demonstrating how these operators work, in practice there is an easier way.
The conditional operator is sometimes called a ternary operator because it involves three operands. The conditional operator is written generally as: Java Code: Conditional Operator Syntax logical_expression ? If the logical_expression evaluates as true, the result of the operation is the value of expression1, and if logical_expression evaluates to false, the result is the value of expression2. You use the switch statement to select from multiple choices that are identified by a set of fixed values for a given expression.
The normal use the switch statement operates rather like a rotary switch in that you can select one of a fixed number of choices. The selection in the switch statement is determined by the value of the expression that you place between the parentheses after the keyword switch. Now when a case label value is equal to the switch expression, the code for that case is executed and followed by the statements for all the other cases that succeed the case that was selected, including that for the default case if that follows. The scope of a variable is the part of the program over which the variable name can be referenced ? in other words, where you can use the variable in the program. A variable does not exist before its declaration; you can refer to it only after it has been declared.
In general, a loop has two parts to it: it has a loop body, which is the code that is to be repeated and can be a single statement or a block of statements, and it has a loop control mechanism that determines how many times the loop body should execute.
Execution of this loop continues as long as the condition you specify in the second part of the control mechanism, the loop_condition, is true. This for loop has two control elements separated by a colon that appear between the parentheses following the for keyword.
This loop is similar to the while loop, except that the expression controlling the loop is tested at the end of the loop block. The two versions of the for loop have quite different mechanisms controlling the number of iterations. The continue statement is executed in this example when i is an exact multiple of 3, causing the rest of the current loop iteration to be skipped. The labeled break enables you to break out to the statement following an enclosing block or loop that has an identifying label, regardless of how many levels of nested blocks there are. When you want to confirm that a certain condition is being meant before continuing with the execution of a method, we use an assertion.
Here, assert is a keyword, and logical_expression is any expression that results in a value of true or false.
In this chapter you have learned about all of the essential mechanisms for making decisions in Java.
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By clicking Confirm bid, you are committing to buy this item from the seller if you are the winning bidder and have read and agree to the Global Shipping Program terms and conditions - opens in a new window or tab. By clicking 1 Click Bid, you commit to buy this item from the seller if you're the winning bidder. We will describe the different type of loop constructs and how to use them and then go into decision logic and how it is used within Java. The data values you are comparing can be variables, constants, or expressions with values drawn from Java's primitive data types (i.e. Note that if the left and right operands of a relational operator are of differing types, values are promoted in the same way as you saw in the previous chapter for mixed arithmetic expressions.
If the remainder isn't equal to 0, the value of number is odd, so you add 1 to make it even. This applies to the statements within a statement block, so you can always nest a statement block between braces inside another statement block, and you can do this to any depth.
This provides an alternative choice of statement, or statement block, that is executed when the expression in the if statement is false. You can apply this in a console program and try out the random() method from the Math class at the same time. This method compares the value in season with the value between the parentheses and results in true if they are equal or false if they are unequal.
You address these cases as well as using logical operators to combine several expressions that have a value true or false. For example, you can have a value being tested that must be both greater than or equal to 'A' AND less than or equal to 'Z'.
It is a good idea to add parentheses if they make the code easier to read and to help to avoid mistakes. Equally, in some instances, you want to be certain the right-hand operand won't be evaluated if the left operand is false.
When both operands have the same value, either both true or both false, the result is false. So if the value of a boolean variable state is true then the expression !state has the value false, and if it is false, then the state evaluates to true.
The standard Java packages provide a range of standard methods to do the sort of testing for particular sets of characters such as letters or digits that you have been doing with if statements.
The isUpperCase() method returns true if the char value that you pass to it is uppercase, and false if it is not. Note that if expression1 is evaluated because logical_expression is true, then expression2 is not, and vice versa. The expression that selects a choice must produce a result of an integer type other than long, or a value of an enumeration type, or a string.
For example, on some makes of washing machine you choose between the various machine settings in this way, with positions for cotton, wool, synthetic fiber, and so on, which you select by turning the knob to point to the option that you want. In this case it's simply the integer variable wash that would need to be previously declared as of type char, byte, short, or int.
If one matches then the code for that case is executed, and the break branches to the first statement after the switch.
Every variable that we have declared so far in the examples has been defined within the context of a method, the method main(). It continues to exist until the end of the block in which it is defined, and that includes any blocks nested within the block containing its declaration.
Local variables are accessible only from the point in the program where they are declared to the end of the block that contains the declaration.
The for loop statement on the third line causes the statements in the following block to be repeated eight times. This expression is checked at the beginning of each loop iteration, and as long as it is true, the loop body executes.
The first element is an identifier of the type that you specify, and the second is an expression specifying a collection of objects or values of the specified type.
When expression is false, the loop ends and execution continues with the statement following the loop block. This means that the loop body always executes at least once, even if the expression is always false. You can also see quite clearly that the primary difference between the while loop and the do-while loop is where the test is carried out. This may be needed when you are calculating the value of a function for a range of fractional values. Suppose you want to sum the values of the integers from 1 to some limit, except that you don't want to include integers that are multiples of three. Program execution continues with the next iteration if there is one, and if not, with the statement following the end of the loop block. Its effect is to exit the switch block and continue execution with the first statement after the switch. This enables you to jump immediately to the statement following the end of any enclosing statement block or loop that is identified by the label in the labeled break statement. You might have several loops nested one within the other, for example, where you could use the labeled break to exit from the innermost loop (or indeed any of them) to the statement following the outermost loop. When this statement executes, if logical_expression evaluates to true, then the program continues normally.


An assertion with the logical expression as false always asserts and terminates the program.
If logical_ expression is false then the program terminates with an error message including the string that results from string_expression.
You have also learned all of the looping facilities that you have available when programming in Java. To start contributing, enable JavaScript by changing your browser options, then try again. Contact the seller- opens in a new window or tab and request a shipping method to your location. Import charges previously quoted are subject to change if you increase you maximum bid amount.
This is part of a larger series of articles to help you prepare for the java associate exam. Whatever decision you make in programming terms requires the ability to make comparisons between variables, constants, and the values of expressions and then execute one group of statements or another, depending on the result of a given comparison. The ability to use a block wherever you can have a statement means that you can use a statement block within the basic if statement that you just saw.
It is easy to convince yourself that the logic is as indicated by the indentation, even when this is completely wrong.
Thus the exclusive OR operator is useful on those rare occasions when you want to establish whether or not two boolean values are different. They are all available within the Character class, which is automatically available in your programs.
Similarly, the isLowerCase() method returns true if the char value you pass to it is lowercase. You can use the conditional operator in lots of circumstances, and one common application of it is to control output, depending on the result of an expression or the value of a variable. Thus, the expression that controls a switch statement can result in a value of type char, byte, short, or int, an enumeration constant, or a String object. You define the possible switch options by one or more case values, also called case labels, which you define using the keyword case. Variables that are declared within a method are called local variables, as they are only accessible within the confines of the method in which they are declared. If the program for the company payroll had to include separate statements to do the calculation for each employee, it would never get written.
The number of times it is to be repeated is determined by the stuff between parentheses following the keyword for. When loop_condition is false, the loop ends and execution continues with the statement following the loop block. The loop executes once for each item of the specified type that appears in the collection, and you can refer to the current item in the loop body using the identifier that you specified as the first control element. The expression is tested at the beginning of the loop, so if it is initially false, the loop body is not executed at all. Suppose you want to calculate the area of a circle with values for the radius from 1 to 2 in steps of 0.2.
You just need to add a label to the beginning of the relevant block or loop that you want to break out of, and use that label in the break statement.
Suppose you have a variable of type int that stores the number of days in the current month. If you reside in an EU member state besides UK, import VAT on this purchase is not recoverable. The previous article that you might want to read is, ?Tutorial:Review of Java Arrays for the Java Certification Exam?. Thus, the first step to understanding how you make decisions in a program is to look at how you make comparisons.
You can continue nesting ifs one inside the other like this for as long as you still know what you are doing or even beyond if you enjoy confusion.
You can vary a message by selecting one text string or another depending on the condition specified. In general, a case label consists of the case keyword followed by a constant value that is the value that selects the case, followed by a colon. However, they are not necessarily accessible everywhere in the code for the method in which they are declared. The point is that you could, in theory, repeat the same block of statements as many times as you want.
When break is executed within a loop, the loop ends immediately, and execution continues with the first statement following the loop. The variable m exists only within the inner block because that's where its declaration appears.
The primary purpose of the for loop is to execute a block of statements a given number of times.
This expression is true if the variable yesNo contains 'y' or 'y,' so yesNo might hold a character entered from the keyboard in this instance. Finally there is also a labeled continue statement that you can use to stop executing an inner loop. After the brace at the end of the inner block, m no longer exists so you can't refer to it. The variable n is still around, though, and it survives until the closing brace of the outer block.



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