wordpress 分享主题,做网站优化有必要,朔州做网站的公司,外链网站本章概要
随机生成泛型和基本数组
随机生成
我们可以按照 Count.java 的结构创建一个生成随机值的工具#xff1a; Rand.java import java.util.*;
import java.util.function.*;import static com.example.test.ConvertTo.primitive;public interface Rand {int MOD 10_0…本章概要
随机生成泛型和基本数组
随机生成
我们可以按照 Count.java 的结构创建一个生成随机值的工具 Rand.java import java.util.*;
import java.util.function.*;import static com.example.test.ConvertTo.primitive;public interface Rand {int MOD 10_000;class Boolean implements Supplierjava.lang.Boolean {SplittableRandom r new SplittableRandom(47);Overridepublic java.lang.Boolean get() {return r.nextBoolean();}public java.lang.Boolean get(int n) {return get();}public java.lang.Boolean[] array(int sz) {java.lang.Boolean[] result new java.lang.Boolean[sz];Arrays.setAll(result, n - get());return result;}}class Pboolean {public boolean[] array(int sz) {return primitive(new Boolean().array(sz));}}class Byteimplements Supplierjava.lang.Byte {SplittableRandom r new SplittableRandom(47);Overridepublic java.lang.Byte get() {return (byte) r.nextInt(MOD);}public java.lang.Byte get(int n) {return get();}public java.lang.Byte[] array(int sz) {java.lang.Byte[] result new java.lang.Byte[sz];Arrays.setAll(result, n - get());return result;}}class Pbyte {public byte[] array(int sz) {return primitive(new Byte().array(sz));}}class Characterimplements Supplierjava.lang.Character {SplittableRandom r new SplittableRandom(47);Overridepublic java.lang.Character get() {return (char) r.nextInt(a, z 1);}public java.lang.Character get(int n) {return get();}public java.lang.Character[] array(int sz) {java.lang.Character[] result new java.lang.Character[sz];Arrays.setAll(result, n - get());return result;}}class Pchar {public char[] array(int sz) {return primitive(new Character().array(sz));}}class Shortimplements Supplierjava.lang.Short {SplittableRandom r new SplittableRandom(47);Overridepublic java.lang.Short get() {return (short) r.nextInt(MOD);}public java.lang.Short get(int n) {return get();}public java.lang.Short[] array(int sz) {java.lang.Short[] result new java.lang.Short[sz];Arrays.setAll(result, n - get());return result;}}class Pshort {public short[] array(int sz) {return primitive(new Short().array(sz));}}class Integerimplements Supplierjava.lang.Integer {SplittableRandom r new SplittableRandom(47);Overridepublic java.lang.Integer get() {return r.nextInt(MOD);}public java.lang.Integer get(int n) {return get();}public java.lang.Integer[] array(int sz) {int[] primitive new Pint().array(sz);java.lang.Integer[] result new java.lang.Integer[sz];for (int i 0; i sz; i) {result[i] primitive[i];}return result;}}class Pint implements IntSupplier {SplittableRandom r new SplittableRandom(47);Overridepublic int getAsInt() {return r.nextInt(MOD);}public int get(int n) {return getAsInt();}public int[] array(int sz) {return r.ints(sz, 0, MOD).toArray();}}class Long implements Supplierjava.lang.Long {SplittableRandom r new SplittableRandom(47);Overridepublic java.lang.Long get() {return r.nextLong(MOD);}public java.lang.Long get(int n) {return get();}public java.lang.Long[] array(int sz) {long[] primitive new Plong().array(sz);java.lang.Long[] result new java.lang.Long[sz];for (int i 0; i sz; i) {result[i] primitive[i];}return result;}}class Plong implements LongSupplier {SplittableRandom r new SplittableRandom(47);Overridepublic long getAsLong() {return r.nextLong(MOD);}public long get(int n) {return getAsLong();}public long[] array(int sz) {return r.longs(sz, 0, MOD).toArray();}}class Floatimplements Supplierjava.lang.Float {SplittableRandom r new SplittableRandom(47);Overridepublic java.lang.Float get() {return (float) trim(r.nextDouble());}public java.lang.Float get(int n) {return get();}public java.lang.Float[] array(int sz) {java.lang.Float[] result new java.lang.Float[sz];Arrays.setAll(result, n - get());return result;}}class Pfloat {public float[] array(int sz) {return primitive(new Float().array(sz));}}static double trim(double d) {return((double) Math.round(d * 1000.0)) / 100.0;}class Double implements Supplierjava.lang.Double {SplittableRandom r new SplittableRandom(47);Overridepublic java.lang.Double get() {return trim(r.nextDouble());}public java.lang.Double get(int n) {return get();}public java.lang.Double[] array(int sz) {double[] primitive new Rand.Pdouble().array(sz);java.lang.Double[] result new java.lang.Double[sz];for (int i 0; i sz; i) {result[i] primitive[i];}return result;}}class Pdouble implements DoubleSupplier {SplittableRandom r new SplittableRandom(47);Overridepublic double getAsDouble() {return trim(r.nextDouble());}public double get(int n) {return getAsDouble();}public double[] array(int sz) {double[] result r.doubles(sz).toArray();Arrays.setAll(result,n - result[n] trim(result[n]));return result;}}class Stringimplements Supplierjava.lang.String {SplittableRandom r new SplittableRandom(47);private int strlen 7; // Default lengthpublic String() {}public String(int strLength) {strlen strLength;}Overridepublic java.lang.String get() {return r.ints(strlen, a, z 1).collect(StringBuilder::new,StringBuilder::appendCodePoint,StringBuilder::append).toString();}public java.lang.String get(int n) {return get();}public java.lang.String[] array(int sz) {java.lang.String[] result new java.lang.String[sz];Arrays.setAll(result, n - get());return result;}}
}ConvertTo.java public interface ConvertTo {static boolean[] primitive(Boolean[] in) {boolean[] result new boolean[in.length];for (int i 0; i in.length; i) {result[i] in[i]; // Autounboxing}return result;}static char[] primitive(Character[] in) {char[] result new char[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static byte[] primitive(Byte[] in) {byte[] result new byte[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static short[] primitive(Short[] in) {short[] result new short[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static int[] primitive(Integer[] in) {int[] result new int[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static long[] primitive(Long[] in) {long[] result new long[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static float[] primitive(Float[] in) {float[] result new float[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static double[] primitive(Double[] in) {double[] result new double[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}// Convert from primitive array to wrapped array:static Boolean[] boxed(boolean[] in) {Boolean[] result new Boolean[in.length];for (int i 0; i in.length; i) {result[i] in[i]; // Autoboxing}return result;}static Character[] boxed(char[] in) {Character[] result new Character[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static Byte[] boxed(byte[] in) {Byte[] result new Byte[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static Short[] boxed(short[] in) {Short[] result new Short[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static Integer[] boxed(int[] in) {Integer[] result new Integer[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static Long[] boxed(long[] in) {Long[] result new Long[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static Float[] boxed(float[] in) {Float[] result new Float[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}static Double[] boxed(double[] in) {Double[] result new Double[in.length];for (int i 0; i in.length; i) {result[i] in[i];}return result;}
}对于除了 int 、 long 和 double 之外的所有基本类型元素生成器只生成数组而不是 Count 中看到的完整操作集。这只是一个设计选择因为本书不需要额外的功能。
下面是对所有 Rand 工具的测试 TestRand.java import java.util.*;
import java.util.stream.*;import static com.example.test.ArrayShow.show;public class TestRand {static final int SZ 5;public static void main(String[] args) {System.out.println(Boolean);Boolean[] a1 new Boolean[SZ];Arrays.setAll(a1, new Rand.Boolean()::get);show(a1);a1 Stream.generate(new Rand.Boolean()).limit(SZ 1).toArray(Boolean[]::new);show(a1);a1 new Rand.Boolean().array(SZ 2);show(a1);boolean[] a1b new Rand.Pboolean().array(SZ 3);show(a1b);System.out.println(Byte);Byte[] a2 new Byte[SZ];Arrays.setAll(a2, new Rand.Byte()::get);show(a2);a2 Stream.generate(new Rand.Byte()).limit(SZ 1).toArray(Byte[]::new);show(a2);a2 new Rand.Byte().array(SZ 2);show(a2);byte[] a2b new Rand.Pbyte().array(SZ 3);show(a2b);System.out.println(Character);Character[] a3 new Character[SZ];Arrays.setAll(a3, new Rand.Character()::get);show(a3);a3 Stream.generate(new Rand.Character()).limit(SZ 1).toArray(Character[]::new);show(a3);a3 new Rand.Character().array(SZ 2);show(a3);char[] a3b new Rand.Pchar().array(SZ 3);show(a3b);System.out.println(Short);Short[] a4 new Short[SZ];Arrays.setAll(a4, new Rand.Short()::get);show(a4);a4 Stream.generate(new Rand.Short()).limit(SZ 1).toArray(Short[]::new);show(a4);a4 new Rand.Short().array(SZ 2);show(a4);short[] a4b new Rand.Pshort().array(SZ 3);show(a4b);System.out.println(Integer);int[] a5 new int[SZ];Arrays.setAll(a5, new Rand.Integer()::get);show(a5);Integer[] a5b Stream.generate(new Rand.Integer()).limit(SZ 1).toArray(Integer[]::new);show(a5b);a5b new Rand.Integer().array(SZ 2);show(a5b);a5 IntStream.generate(new Rand.Pint()).limit(SZ 1).toArray();show(a5);a5 new Rand.Pint().array(SZ 3);show(a5);System.out.println(Long);long[] a6 new long[SZ];Arrays.setAll(a6, new Rand.Long()::get);show(a6);Long[] a6b Stream.generate(new Rand.Long()).limit(SZ 1).toArray(Long[]::new);show(a6b);a6b new Rand.Long().array(SZ 2);show(a6b);a6 LongStream.generate(new Rand.Plong()).limit(SZ 1).toArray();show(a6);a6 new Rand.Plong().array(SZ 3);show(a6);System.out.println(Float);Float[] a7 new Float[SZ];Arrays.setAll(a7, new Rand.Float()::get);show(a7);a7 Stream.generate(new Rand.Float()).limit(SZ 1).toArray(Float[]::new);show(a7);a7 new Rand.Float().array(SZ 2);show(a7);float[] a7b new Rand.Pfloat().array(SZ 3);show(a7b);System.out.println(Double);double[] a8 new double[SZ];Arrays.setAll(a8, new Rand.Double()::get);show(a8);Double[] a8b Stream.generate(new Rand.Double()).limit(SZ 1).toArray(Double[]::new);show(a8b);a8b new Rand.Double().array(SZ 2);show(a8b);a8 DoubleStream.generate(new Rand.Pdouble()).limit(SZ 1).toArray();show(a8);a8 new Rand.Pdouble().array(SZ 3);show(a8);System.out.println(String);String[] s new String[SZ - 1];Arrays.setAll(s, new Rand.String()::get);show(s);s Stream.generate(new Rand.String()).limit(SZ).toArray(String[]::new);show(s);s new Rand.String().array(SZ 1);show(s);Arrays.setAll(s, new Rand.String(4)::get);show(s);s Stream.generate(new Rand.String(4)).limit(SZ).toArray(String[]::new);show(s);s new Rand.String(4).array(SZ 1);show(s);}
}ArrayShow.java import java.util.*;public interface ArrayShow {static void show(Object[] a) {System.out.println(Arrays.toString(a));}static void show(boolean[] a) {System.out.println(Arrays.toString(a));}static void show(byte[] a) {System.out.println(Arrays.toString(a));}static void show(char[] a) {System.out.println(Arrays.toString(a));}static void show(short[] a) {System.out.println(Arrays.toString(a));}static void show(int[] a) {System.out.println(Arrays.toString(a));}static void show(long[] a) {System.out.println(Arrays.toString(a));}static void show(float[] a) {System.out.println(Arrays.toString(a));}static void show(double[] a) {System.out.println(Arrays.toString(a));}// Start with a description:static void show(String info, Object[] a) {System.out.print(info : );show(a);}static void show(String info, boolean[] a) {System.out.print(info : );show(a);}static void show(String info, byte[] a) {System.out.print(info : );show(a);}static void show(String info, char[] a) {System.out.print(info : );show(a);}static void show(String info, short[] a) {System.out.print(info : );show(a);}static void show(String info, int[] a) {System.out.print(info : );show(a);}static void show(String info, long[] a) {System.out.print(info : );show(a);}static void show(String info, float[] a) {System.out.print(info : );show(a);}static void show(String info, double[] a) {System.out.print(info : );show(a);}
}注意除了 String 部分之外这段代码与 TestCount.java 中的代码相同Count 被 Rand 替换。
泛型和基本数组
在本章的前面我们被提醒泛型不能和基元一起工作。在这种情况下我们必须从基元数组转换为包装类型的数组并且还必须从另一个方向转换。ConvertTo.java是一个转换器可以同时对所有类型的数据执行操作。
primitive() 的每个版本都创建一个准确长度的适当基元数组然后从包装类的 in 数组中复制元素。如果任何包装的数组元素是 null 你将得到一个异常这是合理的—否则无法选择有意义的值进行替换)。注意在这个任务中自动装箱如何发生。
下面是对 ConvertTo 中所有方法的测试
import java.util.*;import static com.example.test.ArrayShow.show;
import static com.example.test.ConvertTo.boxed;
import static com.example.test.ConvertTo.primitive;public class TestConvertTo {static final int SIZE 6;public static void main(String[] args) {Boolean[] a1 new Boolean[SIZE];Arrays.setAll(a1, new Rand.Boolean()::get);boolean[] a1p primitive(a1);show(a1p, a1p);Boolean[] a1b boxed(a1p);show(a1b, a1b);Byte[] a2 new Byte[SIZE];Arrays.setAll(a2, new Rand.Byte()::get);byte[] a2p primitive(a2);show(a2p, a2p);Byte[] a2b boxed(a2p);show(a2b, a2b);Character[] a3 new Character[SIZE];Arrays.setAll(a3, new Rand.Character()::get);char[] a3p primitive(a3);show(a3p, a3p);Character[] a3b boxed(a3p);show(a3b, a3b);Short[] a4 new Short[SIZE];Arrays.setAll(a4, new Rand.Short()::get);short[] a4p primitive(a4);show(a4p, a4p);Short[] a4b boxed(a4p);show(a4b, a4b);Integer[] a5 new Integer[SIZE];Arrays.setAll(a5, new Rand.Integer()::get);int[] a5p primitive(a5);show(a5p, a5p);Integer[] a5b boxed(a5p);show(a5b, a5b);Long[] a6 new Long[SIZE];Arrays.setAll(a6, new Rand.Long()::get);long[] a6p primitive(a6);show(a6p, a6p);Long[] a6b boxed(a6p);show(a6b, a6b);Float[] a7 new Float[SIZE];Arrays.setAll(a7, new Rand.Float()::get);float[] a7p primitive(a7);show(a7p, a7p);Float[] a7b boxed(a7p);show(a7b, a7b);Double[] a8 new Double[SIZE];Arrays.setAll(a8, new Rand.Double()::get);double[] a8p primitive(a8);show(a8p, a8p);Double[] a8b boxed(a8p);show(a8b, a8b);}
}在每种情况下原始数组都是为包装类型创建的并使用 Arrays.setAll() 填充正如我们在 TestCouner.java 中所做的那样这也验证了 Arrays.setAll() 是否能同 Integer Long 和 Double 。然后 ConvertTo.primitive() 将包装器数组转换为对应的基元数组ConverTo.boxed() 将其转换回来。
