Declarations and Access Control
Declarations and Access Control |
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Declarations and Access Control
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The following character sequences, formed from ASCII letters, are reserved for use as keywords and cannot be used as identifiers. 1. ẺàÃÕ§ÍÑ¡Éà : 49 Java Keywords abstract boolean break byte case catch char class const continue default do double else extends final finally float for goto if implements import instanceof int interface long native new package private protected public return short static strictfp super switch synchronized this throw throws transient try void volatile while assert
1. Access Modifiers . private Makes a method or a variable accessible only from within its own class. . protected Makes a method or a variable accessible only to classes in the same package or subclasses of the class. . public Makes a class, method, or variable accessible from any other class. 2. Class, Method, and Variable Modifiers . abstract Used to declare a class that cannot be instantiated, or a method that must be implemented by a nonabstract subclass. . class Keyword used to specify a class. . extends Used to indicate the superclass that a subclass is extending. . final Makes it impossible to extend a class, override a method, or reinitialize a variable. . implements Used to indicate the interfaces that a class will implement. . interface Keyword used to specify an interface. . native Indicates a method is written in a platform-dependent language, such as C. . new Used to instantiate an object by invoking the constructor. . static Makes a method or a variable belong to a class as opposed to an instance. . strictfp Used in front of a method or class to indicate that floating-point numbers will follow FP-strict rules in all expressions. . synchronized Indicates that a method can be accessed by only one thread at a time. . transient Prevents fields from ever being serialized. Transient fields are always skipped when objects are serialized. . volatile Indicates a variable may change out of sync because it is used in threads. 3. Flow Control . break Exits from the block of code in which it resides. . case Executes a block of code, dependent on what the switch tests for. . continue Stops the rest of the code following this statement from executing in a loop and then begins the next iteration of the loop. . default Executes this block of code if none of the switch-case statements match. . do Executes a block of code one time, then, in conjunction with the while statement, it performs a test to determine whether the block should be executed again. . else Executes an alternate block of code if an if test is false. . for Used to perform a conditional loop for a block of code. . if Used to perform a logical test for true or false. . instanceof Determines whether an object is an instance of a class, superclass, or interface. . return Returns from a method without executing any code that follows the statement (can optionally return a variable). . switch Indicates the variable to be compared with the case statements. . while Executes a block of code repeatedly while a certain condition is true. 4. Error Handling . catch Declares the block of code used to handle an exception. . finally Block of code, usually following a try-catch statement, which is executed no matter what program flow occurs when dealing with an exception. . throw Used to pass an exception up to the method that called this method. . throws Indicates the method will pass an exception to the method that called it. . try Block of code that will be tried, but which may cause an exception. . assert Evaluates a conditional expression to verify the programmer’s assumption. 5. Package Control . import Statement to import packages or classes into code. . package Specifies to which package all classes in a source file belong. 6. Primitives . boolean A value indicating true or false. . byte An 8-bit integer (signed). . char A single Unicode character (16-bit unsigned) . double A 64-bit floating-point number (signed). . float A 32-bit floating-point number (signed). . int A 32-bit integer (signed). . long A 64-bit integer (signed). . short A 16-bit integer (signed). 7. Variable Keywords . super Reference variable referring to the immediate superclass. . this Reference variable referring to the current instance of an object. 8. Void Return Type Keyword . void Indicates no return type for a method. 9. Unused Reserved Words . const Do not use to declare a constant; use public static final. . goto Not implemented in the Java language. It’s considered harmful. | |||||||||
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