Java Supplier API (#145)

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under the terms of the [MIT
license](https://github.com/dafny-lang/dafny/blob/master/LICENSE.txt).

Author: stefan-aws

docs/java/BuildTest.java

@@ -70,7 +70,7 @@ public static void main(String[] args) {
         System.out.println("\nCUSTOM RNG TESTS\n");
 
         SecureRandom rng = new SecureRandom();
-        DafnyVMC.Random t = new DafnyVMC.Random(rng);
+        DafnyVMC.Random t = new DafnyVMC.Random(() -> rng);
 
         System.out.println("Example of Coin sampling");
         System.out.println(t.CoinSample());

src/interop/java/Full/Random.java

@@ -3,6 +3,7 @@
 import dafny.TypeDescriptor;
 import java.math.BigInteger;
 import java.security.SecureRandom;
+import java.util.function.Supplier;
 
 public class Random implements DafnyVMCTrait.RandomTrait {
   static ThreadLocal<SecureRandom> rng;
@@ -11,8 +12,8 @@ public Random() {
     this.rng = ThreadLocal.withInitial(Random::createSecureRandom);
   }
 
-  public Random(SecureRandom rng) {
-    this.rng = ThreadLocal.withInitial(() -> rng);
+  public Random(Supplier<SecureRandom> supplier) {
+    this.rng = ThreadLocal.withInitial(supplier);
   }
 
   private static final SecureRandom createSecureRandom() {