Enumeration of Java Foundations

Problem: The value of an object's property cannot be arbitrary and must be a fixed set of values for one of the

Workaround:

1) make a judgment in the Setgrade method and throw an exception if it does not conform to the format requirement

2) Restrict user's choice directly, and define user's input by custom class simulation enumeration

Write a grade class, private constructor, providing 5 static constants representing instances of a class

3) A new enumeration type is defined in Jdk5, specifically for solving such problems

4) enumeration is a special Java class that can define properties, methods, constructors, implement interfaces, inherit classes

Packagecn.itcast.enumeration;

Import Org.junit.Test;

Publicclass Demo1 {

@Test

public void Test () {

Print (grade.b);

}

public void print (Grade g)//A B C D E

{

String Value=g.getvalue ();

System.out.println (value);

}

}

/*

* Class grade{Private Grade () {}

* public static final Grade a=new Grade ();

* public static final Grade b=new Grade ();

* public static final Grade c=new Grade ();

* public static final Grade d=new Grade ();

* public static final Grade e=new Grade ();

*  }

*/

How to define constructors, methods, fields for enumerations

Enumgrade {//class A 100-90 B 89-80 C 79-70 D 69-60 E 59-0

A ("100-90"), B ("89-80"), C ("79-70"), D ("69-60"), E ("59-0");//Object

private String value;

Private Grade (String value) {

This.value=value;

}

Public String GetValue () {

return this.value;

}

}

Publicclass Demo1 {

@Test

public void Test () {

Print (grade.b); 89-80, Liang

}

public void print (Grade g)//A B C D E

{

String Value=g.getvalue ();

String Value2=g.localevalue ();

System.out.println (value+ "," +value2);

}

}

Enumerations with abstract methods

Enumgrade {//class A 100-90 excellent b89-80 good C 79-70 General D 69-60 difference E 59-0 fail

A ("100-90") {

Public String Localevalue () {

return "excellent";

}

},

B ("89-80") {

Public String Localevalue () {

return "good";

}

},

C ("79-70") {

Public String Localevalue () {

Return "General";

}

},

D ("69-60") {

Public String Localevalue () {

return "poor";

}

},

E ("59-0") {

Public String Localevalue () {

Return "Failed";

}

};//Object

private String value;

Private Grade (String value) {

This.value=value;

}

Public String GetValue () {

return this.value;

}

Public abstract String Localevalue ();

}

An enumeration class is a Java class, or you can declare properties, methods, constructors

public enum GRADE4 {

A ("90-100"), B ("80-89"), C ("70-79"), D ("60-69"), E ("0-59");

Privatestring value;

PRIVATEGRADE4 (String value) {

This.value= value;

}

Publicstring GetValue () {

returnvalue;

}

}

An enumeration class is a Java class, or it can inherit abstractions and implement interfaces

public enum GRADE5 {

Abstract class cannot create instance object

A ("90-100") {

New a subclass instance of GRADE5

Publicstring tolocalestring () {

return "excellent";

}

}

, B ("80-89") {

New a subclass instance of GRADE5

Publicstring tolocalestring () {

return "good";

}

}

, C ("70-79") {

New a subclass instance of GRADE5

Publicstring tolocalestring () {

Return "Medium";

}

}

, D ("60-69") {

New a subclass instance of GRADE5

Publicstring tolocalestring () {

return "poor";

}

}

, E ("0-59") {

New a subclass instance of GRADE5

Publicstring tolocalestring () {

Return "Failed";

}

};

Privatestring value;

PRIVATEGRADE5 (String value) {

This.value= value;

}

Publicstring GetValue () {

returnvalue;

}

Provides a method to return local information of an enumeration

A method that does not know how to implement it can be defined as an abstract

Publicabstract String tolocalestring ();

}

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Enumeration of Java Foundations