[Java Plasterer] Java Components 3：Java EnumWritten In The FontAn Example to Know EnumHow to use EnumSet and EnumMapEnum Analysis

  when we to set

some constants for projects, we always use ‘public static final’to set

int or string constants.or sometimes,we can also set the paramters in

properties.when the project starts,we can get the properties to use

them.today,we can use enum (jdk 1.5).

three pieces:

  1. an example to know enum

  2. how to use enumset and enummap

  3. enum analysis

  firstly,we use the enum to implements operation.

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<code>package org.nsg.jdk.testenum;</code>

<code>/**</code>

<code> </code><code>* @description  operationtest.java</code>

<code> </code><code>*</code>

<code> </code><code>* @author bysocket</code>

<code> </code><code>* @date 2015-1-8 6:05:59pm</code>

<code> </code><code>* @version 1.0</code>

<code> </code><code>*/</code>

<code>public class operationtest</code>

<code>{</code>

<code>    </code><code>public static void main(string[] args)</code>

<code>    </code><code>{</code>

<code>        </code><code>double x = 2.0,y=4.0;</code>

<code>        </code><code>for (operation op : operation.values())</code>

<code>            </code><code>system.out.printf("%f %s %f = %f%n", x,op,y,op.apply(x, y));</code>

<code>    </code><code>}</code>

<code>}</code>

<code>enum operation</code>

<code>    </code><code>plus("+")</code>

<code>        </code><code>double apply(double x,double y){return x + y;}</code>

<code>    </code><code>},</code>

<code>    </code><code>minus("-")</code>

<code>        </code><code>double apply(double x,double y){return x - y;}</code>

<code>    </code><code>times("*")</code>

<code>        </code><code>double apply(double x,double y){return x * y;}</code>

<code>    </code><code>divide("/")</code>

<code>        </code><code>double apply(double x,double y){return x / y;}</code>

<code>    </code><code>};</code>

<code>    </code> 

<code>    </code><code>private final string symbol;</code>

<code>    </code><code>operation(string symbol){this.symbol = symbol;}</code>

<code>    </code><code>@override</code>

<code>    </code><code>public string tostring(){return symbol;}</code>

<code>    </code><code>abstract double apply(double x,double y);</code>

  run as java application,we can see the console.the result shows operations

<code>2.000000 + 4.000000 = 6.000000</code>

<code>2.000000 - 4.000000 = -2.000000</code>

<code>2.000000 * 4.000000 = 8.000000</code>

<code>2.000000 / 4.000000 = 0.500000</code>

q:‘the enum is just like class?’ 

a:yep,i think that enum is a nice type.so let us know some methods by apis:

1. firstly,we can

make an abstract method ‘apply()’ ,then set in the constant-specific

class body. its called constant-specific method implementation.

2. we can make constructor with fields to make the enum has vales.(like string or int …)

3. tostring() method

: returns the name of this enum constant, as contained in the

declaration. this method may be overridden, though it typically isn’t

necessary or desirable. an enum type should override this method when a

more programmer-friendly string form exists.

4. ‘vales()’ method :to get all enum objects. and ‘getvalue()’ can get the enum object’ value.

note ‘its easy to

learn how to use.then learn more and study in depth.’ and in real

projects,we can use enums to replace int or string enum pattern.and enum

is also a typesafe enum.

  let us see another example to learn some sets of enum.so lets see it:

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<code>import java.util.enummap;</code>

<code>import java.util.enumset;</code>

<code>import java.util.iterator;</code>

<code>import java.util.map.entry;</code>

<code> </code><code>* @description  weektest.java</code>

<code> </code><code>* @date 2015-1-9 2:55:10pm</code>

<code>public class weektest</code>

<code>        </code><code>enumset&lt;</code><code>week</code><code>&gt; weekset = enumset.allof(week.class);</code>

<code>        </code><code>system.out.println("enumset:");</code>

<code>        </code><code>for (week w : weekset)</code>

<code>            </code><code>system.out.println(w);</code>

<code>        </code> 

<code>        </code><code>enummap&lt;</code><code>week</code><code>, string&gt; weekmap = new enummap&lt;</code><code>week</code><code>, string&gt;(week.class);</code>

<code>        </code><code>weekmap.put(week.mon, "星期一");</code>

<code>        </code><code>weekmap.put(week.tue, "星期二");</code>

<code>        </code><code>weekmap.put(week.wed, "星期三");</code>

<code>        </code><code>system.out.println("enummap:");</code>

<code>        </code><code>for (iterator&lt;</code><code>entry</code><code>&lt;week, string&gt;&gt; iterator = weekmap.entryset().iterator(); iterator.hasnext();)</code>

<code>        </code><code>{</code>

<code>            </code><code>entry&lt;</code><code>week</code><code>, string&gt; weekentry = iterator.next();</code>

<code>            </code><code>system.out.println(weekentry.getkey().name()+":"+weekentry.getvalue());</code>

<code>        </code><code>}</code>

<code>enum week</code>

<code>    </code><code>mon("1"), tue("2"), wed("3"), thu("4"), fri("5"), sat("6"),sun("7");</code>

<code>    </code><code>week(string symbol){this.symbol = symbol;}</code>

we can see in console:

<code>&lt;</code><code>font</code> <code>size</code><code>=</code><code>"4"</code> <code>face</code><code>=</code><code>"宋體"</code><code>&gt;enumset:</code>

<code>1</code>

<code>2</code>

<code>3</code>

<code>4</code>

<code>5</code>

<code>6</code>

<code>7</code>

<code>enummap:</code>

<code>mon:星期一</code>

<code>tue:星期二</code>

<code>wed:星期三</code>

<code>&lt;/</code><code>font</code><code>&gt;</code>

note： enumset or enummap is easy for we to use.and with them，we can use enums easily.

  we use ‘javap -c -private xxx’to know the class:

<code>final class org.nsg.jdk.testenum.week extends java.lang.enum&lt;</code><code>org.nsg.jdk.testenu</code>

<code>m.week&gt; {</code>

<code>  </code><code>public static final org.nsg.jdk.testenum.week mon;</code>

<code>  </code><code>public static final org.nsg.jdk.testenum.week tue;</code>

<code>  </code><code>public static final org.nsg.jdk.testenum.week wed;</code>

<code>  </code><code>public static final org.nsg.jdk.testenum.week thu;</code>

<code>  </code><code>public static final org.nsg.jdk.testenum.week fri;</code>

<code>  </code><code>public static final org.nsg.jdk.testenum.week sat;</code>

<code>  </code><code>public static final org.nsg.jdk.testenum.week sun;</code>

<code>  </code><code>private final java.lang.string symbol;</code>

<code>  </code><code>private static final org.nsg.jdk.testenum.week[] $values;</code>

<code>  </code><code>public static org.nsg.jdk.testenum.week[] values();</code>

  we can see ‘enum is a class.just is a class.’but no extends.