Thinking in java -- Map生成器

首先需要一个拥有两个属性的对象Pair，key 和 value

//: net/mindview/util/Pair.javapackage net.mindview.util;public class Pair<K, V> {    public final K key;    public final V value;    public Pair(K k, V v) {        key = k;        value = v;    }} // /:~

以各种不同的方式，生成MAP对象

//: net/mindview/util/MapData.java// A Map filled with data using a generator object.package net.mindview.util;import java.util.*;public class MapData<K, V> extends LinkedHashMap<K, V> {    // A single Pair Generator:    public MapData(Generator<Pair<K, V>> gen, int quantity) {        for (int i = 0; i < quantity; i++) {            Pair<K, V> p = gen.next();            put(p.key, p.value);        }    }    // Two separate Generators:    public MapData(Generator<K> genK, Generator<V> genV, int quantity) {        for (int i = 0; i < quantity; i++) {            put(genK.next(), genV.next());        }    }    // A key Generator and a single value:    public MapData(Generator<K> genK, V value, int quantity) {        for (int i = 0; i < quantity; i++) {            put(genK.next(), value);        }    }    // An Iterable and a value Generator:    public MapData(Iterable<K> genK, Generator<V> genV) {        for (K key : genK) {            put(key, genV.next());        }    }    // An Iterable and a single value:    public MapData(Iterable<K> genK, V value) {        for (K key : genK) {            put(key, value);        }    }    // Generic convenience methods:    public static <K, V> MapData<K, V> map(Generator<Pair<K, V>> gen,            int quantity) {        return new MapData<K, V>(gen, quantity);    }    public static <K, V> MapData<K, V> map(Generator<K> genK,            Generator<V> genV, int quantity) {        return new MapData<K, V>(genK, genV, quantity);    }    public static <K, V> MapData<K, V> map(Generator<K> genK, V value,            int quantity) {        return new MapData<K, V>(genK, value, quantity);    }    public static <K, V> MapData<K, V> map(Iterable<K> genK, Generator<V> genV) {        return new MapData<K, V>(genK, genV);    }    public static <K, V> MapData<K, V> map(Iterable<K> genK, V value) {        return new MapData<K, V>(genK, value);    }} // /:~

分析上面代码，
1、此类继承LinkedHashMap，拥有父类的方法。
2、有5个构造方法，分别以不同的方式初始化，生成对象。

• A single Pair Generator，
• Two separate Generators，
• A key Generator and a single value，
• An Iterable and a value Generator
• An Iterable and a single value

测试类

package containers;//: containers/MapDataTest.javaimport java.util.*;import net.mindview.util.*;import static net.mindview.util.Print.*;class Letters implements Generator<Pair<Integer, String>>, Iterable<Integer> {    private int size = 9;    private int number = 1;    private char letter = 'A';    public Pair<Integer, String> next() {        return new Pair<Integer, String>(number++, "" + letter++);    }    public Iterator<Integer> iterator() {        return new Iterator<Integer>() {            public Integer next() {                return number++;            }            public boolean hasNext() {                return number < size;            }            public void remove() {                throw new UnsupportedOperationException();            }        };    }}public class MapDataTest {    public static void main(String[] args) {        // Pair Generator:        print(MapData.map(new Letters(), 11));        // Two separate generators:        print(MapData.map(new CountingGenerator.Character(),                new RandomGenerator.String(3), 8));        // A key Generator and a single value:        print(MapData.map(new CountingGenerator.Character(), "Value", 6));        // An Iterable and a value Generator:        print(MapData.map(new Letters(), new RandomGenerator.String(3)));        // An Iterable and a single value:        print(MapData.map(new Letters(), "Pop"));    }} /*     * Output: {1=A, 2=B, 3=C, 4=D, 5=E, 6=F, 7=G, 8=H, 9=I, 10=J, 11=K} {a=YNz,     * b=brn, c=yGc, d=FOW, e=ZnT, f=cQr, g=Gse, h=GZM} {a=Value, b=Value,     * c=Value, d=Value, e=Value, f=Value} {1=mJM, 2=RoE, 3=suE, 4=cUO, 5=neO,     * 6=EdL, 7=smw, 8=HLG} {1=Pop, 2=Pop, 3=Pop, 4=Pop, 5=Pop, 6=Pop, 7=Pop,     * 8=Pop}     */// :~

分析上面代码，Letters类实现Generator和Iterable接口
main方法分别调用不同的构造参数，来生成map对象。

“Thinking in java 17.2.2章节”
下面附上一些一来到的代码

//: net/mindview/util/Generator.java// A generic interface.package net.mindview.util;public interface Generator<T> { T next(); } ///:~

//: net/mindview/util/CountingGenerator.java// Simple generator implementations.package net.mindview.util;public class CountingGenerator {    public static class Boolean implements Generator<java.lang.Boolean> {        private boolean value = false;        public java.lang.Boolean next() {            value = !value; // Just flips back and forth            return value;        }    }    public static class Byte implements Generator<java.lang.Byte> {        private byte value = 0;        public java.lang.Byte next() {            return value++;        }    }    static char[] chars = ("abcdefghijklmnopqrstuvwxyz"            + "ABCDEFGHIJKLMNOPQRSTUVWXYZ").toCharArray();    public static class Character implements Generator<java.lang.Character> {        int index = -1;        public java.lang.Character next() {            index = (index + 1) % chars.length;            return chars[index];        }    }    public static class String implements Generator<java.lang.String> {        private int length = 7;        Generator<java.lang.Character> cg = new Character();        public String() {        }        public String(int length) {            this.length = length;        }        public java.lang.String next() {            char[] buf = new char[length];            for (int i = 0; i < length; i++)                buf[i] = cg.next();            return new java.lang.String(buf);        }    }    public static class Short implements Generator<java.lang.Short> {        private short value = 0;        public java.lang.Short next() {            return value++;        }    }    public static class Integer implements Generator<java.lang.Integer> {        private int value = 0;        public java.lang.Integer next() {            return value++;        }    }    public static class Long implements Generator<java.lang.Long> {        private long value = 0;        public java.lang.Long next() {            return value++;        }    }    public static class Float implements Generator<java.lang.Float> {        private float value = 0;        public java.lang.Float next() {            float result = value;            value += 1.0;            return result;        }    }    public static class Double implements Generator<java.lang.Double> {        private double value = 0.0;        public java.lang.Double next() {            double result = value;            value += 1.0;            return result;        }    }} // /:~

//: net/mindview/util/RandomGenerator.java// Generators that produce random values.package net.mindview.util;import java.util.*;public class RandomGenerator {    private static Random r = new Random(47);    public static class Boolean implements Generator<java.lang.Boolean> {        public java.lang.Boolean next() {            return r.nextBoolean();        }    }    public static class Byte implements Generator<java.lang.Byte> {        public java.lang.Byte next() {            return (byte) r.nextInt();        }    }    public static class Character implements Generator<java.lang.Character> {        public java.lang.Character next() {            return CountingGenerator.chars[r                    .nextInt(CountingGenerator.chars.length)];        }    }    public static class String extends CountingGenerator.String {        // Plug in the random Character generator:        {            cg = new Character();        } // Instance initializer        public String() {        }        public String(int length) {            super(length);        }    }    public static class Short implements Generator<java.lang.Short> {        public java.lang.Short next() {            return (short) r.nextInt();        }    }    public static class Integer implements Generator<java.lang.Integer> {        private int mod = 10000;        public Integer() {        }        public Integer(int modulo) {            mod = modulo;        }        public java.lang.Integer next() {            return r.nextInt(mod);        }    }    public static class Long implements Generator<java.lang.Long> {        private int mod = 10000;        public Long() {        }        public Long(int modulo) {            mod = modulo;        }        public java.lang.Long next() {            return new java.lang.Long(r.nextInt(mod));        }    }    public static class Float implements Generator<java.lang.Float> {        public java.lang.Float next() {            // Trim all but the first two decimal places:            int trimmed = Math.round(r.nextFloat() * 100);            return ((float) trimmed) / 100;        }    }    public static class Double implements Generator<java.lang.Double> {        public java.lang.Double next() {            long trimmed = Math.round(r.nextDouble() * 100);            return ((double) trimmed) / 100;        }    }} // /:~