OnJava8-Examples/collectiontopics/StreamFillMaps.java

// collectiontopics/StreamFillMaps.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
import java.util.*;
import java.util.function.*;
import java.util.stream.*;
import onjava.*;

class Letters
implements Supplier<Pair<Integer,String>> {
  private int number = 1;
  private char letter = 'A';
  @Override public Pair<Integer,String> get() {
    return new Pair<>(number++, "" + letter++);
  }
}

public class StreamFillMaps {
  public static void main(String[] args) {
    Map<Integer,String> m =
      Stream.generate(new Letters())
      .limit(11)
      .collect(Collectors
        .toMap(Pair::key, Pair::value));
    System.out.println(m);

    // Two separate Suppliers:
    Rand.String rs = new Rand.String(3);
    Count.Character cc = new Count.Character();
    Map<Character,String> mcs = Stream.generate(
      () -> Pair.make(cc.get(), rs.get()))
      .limit(8)
      .collect(Collectors
        .toMap(Pair::key, Pair::value));
    System.out.println(mcs);

    // A key Supplier and a single value:
    Map<Character,String> mcs2 = Stream.generate(
      () -> Pair.make(cc.get(), "Val"))
      .limit(8)
      .collect(Collectors
        .toMap(Pair::key, Pair::value));
    System.out.println(mcs2);
  }
}
/* Output:
{1=A, 2=B, 3=C, 4=D, 5=E, 6=F, 7=G, 8=H, 9=I, 10=J,
11=K}
{b=btp, c=enp, d=ccu, e=xsz, f=gvg, g=mei, h=nne,
i=elo}
{p=Val, q=Val, j=Val, k=Val, l=Val, m=Val, n=Val,
o=Val}
*/