Download OCA Java SE 8 Programmer Certification Exam Preparation: Key Concepts and Examples and more Exams Nursing in PDF only on Docsity!
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Package statement Import statements Comments Class declaration { Variables Comments Constructors Methods Nested classes Nested interfaces Enum } - Structure of a Java class public final class Runner extends Person implements Athlete {} - Components of a class declaration using an example
- Per Java naming conventions, package names should all be in lowercase.
- The package and subpackage names are separated using a dot (.).
- Package names follow the rules defined for valid identifiers in Java.
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- For classes and interfaces defined in a package, the package statement is the first statement in a Java source file (a .java file). The exception is that comments can appear before or after a package statement.
- There can be a maximum of one package statement per Java source code file (.java file).
- All the classes and interfaces defined in a Java source code file are defined in the same package. They can't be defined in separate packages. - RULES TO REMEMBER Here are a few of important rules about packages Public Protected Default Private - Access modifiers
- Derived/Same pkg
- Derived/Separate pkg
- Unrelated/Same pkg
- Unrelated/Separate pkg - Public access modifiers
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static final synchronized native strictfp transient volatile - Nonaccess modifiers A synchronized method can't be accessed by multiple threads concurrently. You can't mark classes, interfaces, or variables with this modifier - Synchronized nonaccess modifier A native method calls and makes use of libraries and methods implemented in other programming languages such as C or C++. You can't mark classes, interfaces, or variables with this modifier - Native nonaccess modifier A transient variable isn't serialized when the corresponding object is serialized. The transient modifier can't be applied to classes, interfaces, or methods - Transient nonaccess modifier
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A volatile variable's value can be safely modified by different threads. Classes, interfaces, and methods can't use this modifier. - Volatile nonaccess modifier Classes, interfaces, and methods defined using this keyword ensure that calculations using floating-point numbers are identical on all platforms. This modifier can't be used with variables. - Strictfp nonaccess modifier Static variables belong to a class. They're common to all instances of a class and aren't unique to any instance of a class. static attributes exist independently of any instances of a class and may be accessed even when no instances of the class have been created. You can compare a static variable with a shared variable. A static variable is shared by all the objects of a class - Static variables Static methods aren't associated with objects and can't use any of the instance variables of a class. It's a common practice to use static methods to define utility methods, which are methods that usually manipulate the method parameters to compute and return an appropriate value: static double interest(double num1, double num2, double num3) {
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AUTOMATIC MEMORY MANAGEMENT
MULTITHREADING AND CONCURRENCY
SECURITY - Valid features and components of Java Java lets you abstract objects and include only the required properties and behavior in your code. - Abstraction Java enables its classes to inherit other classes and implement interfaces. The interfaces can inherit other interfaces - Inheritance Java enables instances of its classes to exhibit multiple behaviors for the same method calls - Polymorphism Java emulates real-life object definition and behavior. It uses classes, interfaces, or enums to define all its code - Object orientation The state or the fields of a class are protected from unwanted access and manipulation - Encapsulation
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In Java, you must declare a variable with its data type before you can use it - Type safety Java uses garbage collectors for automatic memory management. They reclaim memory from objects that are no longer in use. - Automatic memory management Java defines classes and interfaces to enable developers to develop multithreaded code - Multithreading andconcurrency A variable defined as one of the primitive data types is a primitive variable - Primitive variable char byte short int long float double
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- Instance variables (also known as attributes, fields, and nonstatic variables)
- Class variables (also known as static variables) - Scope of variables ArrayIndexOutOfBoundsException IndexOutOfBoundsException ClassCastException IllegalArgumentException ArithmeticException NullPointerException NumberFormatException - Runtime exceptions ExceptionInInitializerError StackOverflowError NoClassDefFoundError OutOfMemoryError - Errors
