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Java certification - fundamentals
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Keywords are special reserved words in Java that you cannot use as identifiers (names) for classes, methods, or variables. Access Modifiers - private - accessible only from within it's own class
- protected - only to classes in the same package or subclasses of the class.
- public - from any other class
Class, methods, and variable modifiers - abstract - cannot be instantiated, must be implemented by a nonabstract subclass.
- class - keyword that specifies a class
- extends - indicates the superclass that a suclass is extending
- final - impossible to extend a class, override a method, or reinitialize a variable
- implements - indicates the interfaces that a class implements
- interface - specifies the interface
- native - a method is written in a platform-dependent language
- new - instantiating, invoking the constructor
- static - variable belong to a class as opposed to an instance
- strictfp - will follow FP-strict rules in all expressions
- synchronized - method can be accessed only by one thread
- transient - prevents fields from ever being serialized
- volatile - may change out of sync
Flow Control - break - exits from the block of code in which it is
- case - executes a block of code, dependent on the switch
- continue - begins the next iteration of the loop
- default - executes if none of the switch-case statements match
- do - conjuction with the while statement
- else - if an if test is false
- for - conditional loop for a block of code
- if - logical test for true or false
- instanceof - whether an object is an instance of a class, superclass, or interface
- return - returns from method
- switch - variable to be compared with the case statements
- while - repeats while a certain condition is true
Error Handling - catch - declares the block to handle an exception
- finally - is executed no matter what program flow occurs
- throw - used to pass an exception
- throws - indicates the method will pass an exception
- try - block that will be tried, and which may cause an exception
- assert - evaluates an expression to verify the assumption of the programmer
Package control - import - statement that says which packages or classes to import
- package - specifies the package to which the sourcecode belongs
Primitives - boolean - a value true or false
- byte - 8-bit signed integer
- char - unicode character (16-bit)
- short - 16-bit integer which is signed
- double - 64-bit floating-point number which is signed
- float - 32-bit floating-point number which is signed
- int - 32-bit integer number which is signed
- long - 64-bit integer which is signed
Variable keywords - super - refers to the superclass
- this - refers to the current object
Void return type - void - indicates no return type
Unused reserved words - const - use public static final instead
- goto - not implemented !
null, true and false are technically not keywords, but literal values ! Range of the primitives Six number types in Java are signed. The positive range is one less than the negative range. Zero is stored as a positive binary number. Boolean can be only true or false. Most of the ranges are virtual-machine depentent. The char type is a single unsigned 16-bit Unicode character. A primitive literal - is a source code representation of the primitive data types. Integer literals There are three ways how to write an integer primitive: as a - decimal
- octal - by placing the zero in front of the number (up to 21 digits)
- hexadecimal - by the prefix 0x or the optional suffix extension L (up to 16 digits)
Floating point defined as double (64 bits) by default. If you want to use the float, you must attach the suffix F or f to the number. You may also also attach a D or d to touble literals, but it's not necessary. Boolean literals can only be defined as true or false. Character literals char literals are represented by a single character in single quotes. You can use the escape code like \n for a new line. Literal values for Strings strings are not primitives, they can be represented as literals (typed directly into the code) Arrays are objects that store multiple variables of the same type. There are three important steps: - make an array reference (declaration) eg. int test[]; It is recommended to put the brackets after the type.
- construct the array object eg.
- initialize the array
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