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Flow Control and Exception Handling


Write code using if and switch statements and identify legal argument types for these statements.


The if statement

The legal argument type for if statements is a boolean value i.e. true, false or any expression which evaluates to these values. In Java true and false are not represented by integers like in C or C++.

Only one statement can appear after if or else. If you want to include more statements, you will need to create a block using {}. You can also include the curly braces when using the if, even if there is only one statement in each clause. This makes it easy to add another statement at a later time, and you do not have to worry about forgetting the braces.

Nested if statements

When you nest if statements, the main thing to remember is that an else statement always refers to the nearest if statement that is within the same block as the else and that is not already associated with an else.

The if-else-if ladder

The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed. The final else acts as a default condition; that is, if all other conditional tests fail, then the last else statement is performed. If there is no final else and all other conditions are false, then no action will be taken.

The switch statement

It is Java’s multi-way branch statement. It provides an easy way to dispatch execution to different parts of your code based on the value of an expression. As such, it often provides a better alternative than a large series of if-else-if statements.

The switch expression must be of type byte, short, int, or char; each of the values specified in the case statements must be of a type compatible with or assignable to the expression. Each case value must be a constant, not a variable. Duplicate case values are not allowed. A break statement is used inside the switch to terminate a statement sequence. When a break statement is encountered, execution branches to the first line of code that follows the entire switch statement. This has the effect of jumping out of the switch.

The break statement is optional. If it is omitted, execution will continue on into the next case. It is sometimes desirable to have multiple cases without break statements between them.

Nested switch statements

You can use a switch as part of the statement sequence of an outer switch. Since a switch statement defines its own block, no conflicts arise between the case constants in the  inner switch and those in the outer switch.

The important features of switch statement:

  • The switch differs from the if in that switch can test for equality, whereas if can evaluate any type of boolean expression.

  • No two case constants in the same switch can have identical values. Of course, a switch statement enclosed by an outer switch can have case constants in common.

  • A switch statement is usually more efficient than a set of nested ifs.

 


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