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this and super and final

The difference between super and this:

this means that the current generation of objects created
Other constructors call this class: The first line of this constructor (parameter list)
Variables distinction of the same name (and local members) this.
refers to super parent class object
Call the parent class constructor
Default empty constructor calls the parent class
Other constructor calls the parent class to be displayed using the super (parameter list)
To use the first line in the constructor
this does not exist and super constructor call use
Variables with the same name to distinguish (sub-classes and superclasses)
If present, local, sub-class members, the parent class members with the same name issue, calling time
Local calls, direct write
Call the sub-class member, use this.
Call the parent class members, using super.
If the problem with the same name does not exist, corresponding to omitted this. Or super.
Before you create a subclass object, first create the parent object -> Subclass after my late father (parent object subclass object memory space, can not directly operate external, internal use only by super in this subclass the parent class object)
Initial order: first the static member
final final
1. The final variable is a constant modified
If the data type of the basic variable data types: stored data value can not be changed
If the data type of the variable is a reference data type: address storage object can not be changed, but the property value of the target memory can be varied
2. the final modified method can not be overridden
3. the final modified class can not be inherited (eunuch class)
Q: private property, and -> to provide getter, setter can use it ??? can access by setting and operation of the parent class of private property

Three characteristics of object-oriented

Object-oriented three characteristics:

Package: hide implementation details inside and outside to provide a common access method
Inheritance: Once the subclass inherits the parent class, you have the right to use the content of the parent class
Polymorphism: a variety of forms a thing of | a variety of forms
Polymorphic premise: class inheritance | implements the interface
Polymorphic ultimate expression of: subclass object reference points to the parent class
If the child has override methods in parent classes, polymorphic method call is overridden in a subclass
Note: New in reference to the parent class is not visible to subclasses
Use of polymorphic members call:
1) member variables
Compile and run to see the parent class | Look left | see type
2) member methods
Compile see the parent class, subclass run to see
Compile look left, look to the right to run
Compile look at the type of operation to find the object

Rewrite and overloading

The difference between the rewrite and reload: rewriting and methods are overloaded
Overload:
The same class
Multiple methods, the same method name
Different parameter list | different method signature
Rewrite:
1. Different classes
2. inheritance | achieved
3. The same method signature
Why use rewrite:
Demand: There is a subclass inherits from a parent class in function, but the subclass implementation of a function, the parent class is not the same, this method can be function of rewrite
How to use the override method:
In this subclass object using the function call, and if there is a method to rewrite, rewrite method is called, if the rewrite, it will call inherited from the parent class functions
Check whether the override methods:
1) the presence of a method override left upward triangle
2) @Override add annotations on the method, mandatory testing, if not rewrite method on the error
note:
Proprietary content can not be inherited, rewrite
The modified final methods can not be overridden
static content can not be rewritten

 如果子父类中存在方法签名相同的方法,父类中这个方法为static修饰的,子类中的同名方法必须也要被static修饰

tostring and equals method

1.toString () to show the contents of an object as a string

Source:

public String toString() {
        	return getClass().getName() + "@" + Integer.toHexString(hashCode());
    	}

In print an object when the reference, print the address of the object, the object is the default print calls toString method's return value
Requirements: When you want to print an object reference data type a custom quote, print the value of all the member properties of the object, rather than address

2.equals method

Source: *

public boolean equals(Object obj) {  //Object obj=new Person();
        return (this == obj);
    }

The difference between equals and ==:

== address value comparison reference data type
equals () address () method or the comparison target equals Object class if used in
If you have content to rewrite equals () method, you can achieve more objects

instanceof

Transformation:
a strongly typed language
data type transformation
java.lang.ClassCastException abnormal type conversion

To avoid abnormal type conversion introduces an operator instanceof
Instanceof type reference
Determine whether the reference is to an object in front of the back type of | his sub-class object, if the return is true, not false returns

Abstract methods abstract class

Abstract classes: modified class is abstract

Abstract methods: abstract being modified method
There is no way the body can
In the abstract class must
note:
1. abstract class can not be instantiated | can not create object
2. To abstract the presence of an abstract class, an abstract method to be rewritten
3. The use of abstract classes:

 具体子类: 重写所有的抽象方法+ 按需新增

 抽象子类: 按需重写抽象方法 + 按需新增

4. A method abstract been rewritten once, it does not need to be rewritten again
The abstract class there may be an ordinary method, there may be an abstract method
6.abstract not be used with private, final, static, native
father:
Specific parent: the parent object can be created, how the contents of the parent class definition
Abstract parent class:
You do not want to create the parent class object directly
The parent class method body does not know how to achieve

Finishing java study notes