Chapter 6: enumeration and annotation. Item30: Use Enum to replace int constants. & Item32: Use enumset to replace the bit field. & Item33: Use enummap to replace the ordinal index.

1 package COM. twoslow. cha6; 2 3 Import Java. util. hashmap; 4 Import Java. util. map; 5 6 Public Enum operation {7 8 plus ("+") {9 @ override10 double apply (Double X, Double Y) {11 return X + Y; 12} 13}, minus ("-") {14 @ override15 double apply (Double X, Double Y) {16 return x-y; 17} 18 }, times ("*") {19 @ override20 double apply (Double X, Double Y) {21 return x * Y; 22} 23}, divide ("/") {24 @ override25 do Uble apply (Double X, Double Y) {26 return x/y; 27} 28}; 29 30 Private Static final map <string, Operation> stringtoenum = new hashmap <string, operation> (); 31 32 // convert the custom string representation back to the corresponding enumeration. 33 static {34 for (Operation OP: values () {35 stringtoenum. put (op. tostring (), OP); 36} 37} 38 39 public static operation fromstring (string symbol) {40 return stringtoenum. get (Symbol); 41} 42 43 private final string symbol; 44 45 operation (string symbol) {46 this. symbol = symbol; 47} 48 49 Public String tostring () {50 return symbol; 51} 52 53 abstract double apply (Double X, Double Y); 54}

1 public class text {2 Public Enum style {bold, italic, underline, strikethrough} 3 Public void applystyles (set <style> styles ){...} 4 5} 6 // The usage is as follows: 7 text. applystyles (enumset. of (style. bold, style. italic ));

There are many plants in a garden. They are divided into three types: Annual, perennia, and biennia, which correspond to Herb. type.

What we need to do now is traverse every plant in the garden, divide these plants into three categories, and finally print the classification of the plants after classification:

 1 package com.twoslow.cha6; 2  3 public class Herb { 4     public enum Type { ANNUAL, PERENNIAL, BIENNIAL } 5     private final String name; 6     private final Type type; 7      8     Herb(String name, Type type) { 9         this.name = name;10         this.type = type;11     }12     13     @Override 14     public String toString() {15         return name;16     }17 }

 1 public static void main(String[] args) { 2         Herb[] garden = ...; 3         Map<Herb.Type, Set<Herb>> herbsByType =new EnumMap<Herb.Type, Set<Herb>>(Herb.Type.class); 4  5         for (Herb.Type t : Herb.Type.values()) { 6             herbsByType.put(t, new HashSet<Herb>()); 7         } 8         for (Herb h : garden) { 9             herbsByType.get(h.type).add(h);10         }11         System.out.println(herbsByType);12     }

 

Chapter 6: enumeration and annotation. Item30: Use Enum to replace int constants. & Item32: Use enumset to replace the bit field. & Item33: Use enummap to replace the ordinal index.