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41 Cards in this Set

  • Front
  • Back
Java Identifiers
All the Java components-classes, variables, and methods
need names. In Java these names are called identifiers.
Inheritance
Concept of inheritance allows code defined in one class to be reused in other classes.
Interfaces
Interfaces are like a 100-percent abstract superclass that defines the methods a subclass must support, but
not how they must be supported.
Cohesion
High cohesion means a class should only do what it is supposed to do, and does it fully. Do not overload it with functions that it is not supposed to do.
Legal Identifiers
1. Must start with a letter, ( $ ), or ( _ )
2. Cannot start with a number
3. Can contain numbers after the first character.
4. No limit to the number of characters.
5. Java built-in keywords can not be used as identifiers.
Constants
Java constants are created by marking variables static and
final.
JavaBeans
JavaBeans are Java classes that have properties
JavaBean Property Naming Rules
Non-boolean property, the getter method's prefix must be "get".
Boolean property, the getter method's prefix is either "get" or "is".
Setter method's prefix must be "set".
getSize(), setSize() & isValid
Class declaration rules
One public class per source code file.
Name of the file must match the name of the public class.
Comments can appear anywhere in the source code file.
package statement, import statement(s), class declaration
import and package statements apply to all classes within a source code file.
A file can have more than one nonpublic class.
Files with no public classes can have a name that does not match any of the classes in the file.
Class can be declared with only public or
default access
Modifiers
Access modifiers: public, protected, private.
Non-access modifiers: abstract, final, strictfp.
Class - Default Access
default access is a package-level access, because a class with default access can be seen only by classes within the same package.
Class Other - Nonaccess Class Modifiers
final, abstract, or strictfp
final and abstract cannot be used together
strictfp
any method code in the class will conform to the IEEE 754 standard rules for floating points.
final class
final class cannot be sub-classed (extend)
abstract class
abstract class can never be instantiated, it is only to be sub-classed
abstract class Car {
private double price;
private String model;
private String year;
public abstract void goFast();
public abstract void goUpHill();
public abstract void impressNeighbors();
}
Methods marked abstract end in a semicolon rather than curly braces.
An abstract class can have both abstract and non-abstract methods.
interface class declaration
public abstract interface Rollable { }
Is this legal interface declaration?
Yes, but typing in the abstract modifier is considered redundant. So both of these declarations are identical:
public abstract interface Rollable { }
public interface Rollable { }
interface methods
All interface methods are implicitly public and abstract
void methodName(); will be
public abstract void methodName();
interface variables
All variables defined in an interface must be public, static, and final, in other words, interfaces can declare only constants, not instance variables.
So int BAR = 42; will be
public static final int BAR = 42;
Interface methods can be static?
No
Interface methods can be marked final, strictfp, or native?
No
Interface can be extended?
Yes
Interface can be extended by another class?
No, Interface can be extended by another interface only.
Can interface implement another interface or class?
No, an interface cannot implement another interface or class.
Class member access modifiers?
public, protected, default, private
Difference between default and protected class members?
A default member may be accessed only if the class accessing the member belongs to the same package, whereas a protected member can be accessed (through inheritance) by a subclass even if the subclass is in a different package.
Can access modifiers be applied to local variables?
No
Which access modifier can be applied to local variables?
final
What are non-access method modifiers?
final, abstract, static, transient, synchronized, native, strictfp
Can method arguments be declared as final?
Yes
abstract modifier can be combined with static for methods?
No
What are synchronized methods?
Synchronized method can be accessed by only one thread at a time.
Native modifier can be applied to class, method and variables?
No, native modifier can be applied only to methods.
Difference between arguments and parameters
arguments: Things between parentheses while invoking method
parameters: Things in the method's signature
What is ellipsis?
(...)
How to write method with var-args
void doStuff(int... x) { }
Can a constructor have a return type?
No
Which modifiers are restricted for constructor?
static, final, abstract
Types of variables
Primitive and reference variables
List of primitives
char, boolean, byte, short, int, long, double, float
What are instance variables?
Instance variables are defined inside the class but outside any method and are only initialized when the class instantiates.
nothing