code 39 barcode generator vb.net Modifier Keywords in VB.NET

Maker Code 128A in VB.NET Modifier Keywords

Tables 4-4, 4-5, and 4-6 contrast the keywords used as modifiers for program elements. We have broken this category down into three topic areas: access modifiers, inheritance-related modifiers, and others.

For comprehensive coverage of each keyword, refer to the "Modifiers" section later in this chapter.

Java C# Comments Identifies a public program element. public public private private Identifies a private program element. protected protected Identifies a protected program element. The protected keyword provides different accessibility in C# than Java. N/A internal Identifies an internal program element providing access to all members of the containing assembly.

Comments Identifies an incomplete implementation of a program element. Identifies an element that cannot be derived from. Identifies an element that hides an inherited member. Identifies an element that overrides an inherited virtual member. Identifies a member that can be overridden by a derived class.

Java C# Comments final readonly Identifies a field that can be assigned to only once. native extern Identifies an externally implemented member. Identifies a static program element. static static N/A C# has no equivalent for the strictfp keyword. strictfp synchronized lock Synchronizes access to a statement block. N/A C# does not provide a language equivalent of transient; however, the transient NonSerialized attribute provides comparable functionality. See 10 for full details. volatile volatile Ensures synchronized and ordered access to a field.

Table 4-7 contrasts the Java and C# keywords used to provide conditional and flow control capabilities.

See the "Statements" section later in this chapter for a full description of the keywords in Table 4-7.

Comments C# alternatives are implemented through static members of the Trace and Debug classes in the .NET class libraries. Conditional statement. if if Optional component of the if statement. else else switch switch Conditional statement. Component of the switch statement. case case default default Optional component of the switch statement. Determinant loop. for for Postloop conditional. do do Preloop conditional. while while

foreach Collection-specific enumerator. Part of the foreach statement. in Java reserved keyword (unused). Provides unconditional branching support goto in C#. continue continue Start a new iteration of a loop. break break Terminate a loop. return return Return from a functional member.

Exception handling is predominantly the same in C# and Java, although declaring exceptions is not required in C#. C# adds keywords used to control how integral arithmetic overflow is handled at compile time and run time. Table 4-8 describes the C# keywords related to exception handling.

For comprehensive coverage of the keywords in Table 4-8, see the "Statements" section later in this chapter and the "Exceptions and Exception Handling" section in 6, "Advanced Language Features."

Comments Encloses a block of code statements. If an exception is thrown by one of these statements, program execution will be transferred to the statements enclosed by a suitable catch block or to the statement immediately following the enclosed statement block. C# also supports general and anonymous catch clauses. catch catch Code to execute regardless of whether a try catch statement block exits finally finally normally or via an exception. Throw or rethrow an exception. throw throw Not supported in C#. throws N/A N/A checked Turns on integral arithmetic overflow checking. N/A unchecked Turns off integral arithmetic overflow checking.

C# introduces four keywords specifically related to the use of unmanaged code, a feature not available in Java. Table 4-9 summarizes these keywords.

Refer to the "Unsafe Code" section in 6 for comprehensive coverage of the keywords in Table 4-9.

Comments Allows a pointer to reference a managed variable, ensuring that the garbage collector does not relocate or deallocate the variable while it's still referenced. N/A sizeof Gets the size in bytes of the memory occupied by a value type instance. See the section "Unsafe Code" in 6 for details. N/A stackalloc Allocates memory blocks on the stack for the storage of local variables. N/A unsafe Identifies unsafe types, members, statements, or code blocks.