--- jsr166/src/jsr166y/ThreadLocalRandom.java 2009/07/20 21:54:51 1.4 +++ jsr166/src/jsr166y/ThreadLocalRandom.java 2009/07/31 16:25:20 1.11 @@ -5,19 +5,19 @@ */ package jsr166y; -import java.util.*; + +import java.util.Random; /** - * A random number generator with the same properties as class {@link - * Random} but isolated to the current Thread. Like the global - * generator used by the {@link java.lang.Math} class, a - * ThreadLocalRandom is initialized with an internally generated seed - * that may not otherwise be modified. When applicable, use of - * ThreadLocalRandom rather than shared Random objects in concurrent - * programs will typically encounter much less overhead and - * contention. ThreadLocalRandoms are particularly appropriate when - * multiple tasks (for example, each a {@link ForkJoinTask}), use - * random numbers in parallel in thread pools. + * A random number generator isolated to the current Thread. Like the + * global {@link java.util.Random} generator used by the {@link + * java.lang.Math} class, a ThreadLocalRandom is initialized with an + * internally generated seed that may not otherwise be modified. When + * applicable, use of ThreadLocalRandom rather than shared Random + * objects in concurrent programs will typically encounter much less + * overhead and contention. ThreadLocalRandoms are particularly + * appropriate when multiple tasks (for example, each a {@link + * ForkJoinTask}), use random numbers in parallel in thread pools. * *

Usages of this class should typically be of the form: * {@code ThreadLocalRandom.current().nextX(...)} (where @@ -27,6 +27,9 @@ import java.util.*; * *

This class also provides additional commonly used bounded random * generation methods. + * + * @since 1.7 + * @author Doug Lea */ public class ThreadLocalRandom extends Random { // same constants as Random, but must be redeclared because private @@ -35,7 +38,7 @@ public class ThreadLocalRandom extends R private final static long mask = (1L << 48) - 1; /** - * The random seed. We can't use super.seed + * The random seed. We can't use super.seed. */ private long rnd; @@ -73,7 +76,8 @@ public class ThreadLocalRandom extends R } /** - * Returns the current Thread's ThreadLocalRandom + * Returns the current Thread's ThreadLocalRandom. + * * @return the current Thread's ThreadLocalRandom */ public static ThreadLocalRandom current() { @@ -83,6 +87,7 @@ public class ThreadLocalRandom extends R /** * Throws UnsupportedOperationException. Setting seeds in this * generator is unsupported. + * * @throws UnsupportedOperationException always */ public void setSeed(long seed) { @@ -93,12 +98,14 @@ public class ThreadLocalRandom extends R } protected int next(int bits) { - return (int)((rnd = (rnd * multiplier + addend) & mask) >>> (48-bits)); + rnd = (rnd * multiplier + addend) & mask; + return (int) (rnd >>> (48-bits)); } /** * Returns a pseudorandom, uniformly distributed value between the * given least value (inclusive) and bound (exclusive). + * * @param least the least value returned * @param bound the upper bound (exclusive) * @throws IllegalArgumentException if least greater than or equal @@ -113,7 +120,8 @@ public class ThreadLocalRandom extends R /** * Returns a pseudorandom, uniformly distributed value - * between 0 (inclusive) and the specified value (exclusive) + * between 0 (inclusive) and the specified value (exclusive). + * * @param n the bound on the random number to be returned. Must be * positive. * @return the next value @@ -131,17 +139,18 @@ public class ThreadLocalRandom extends R while (n >= Integer.MAX_VALUE) { int bits = next(2); long half = n >>> 1; - long nextn = ((bits & 2) == 0)? half : n - half; + long nextn = ((bits & 2) == 0) ? half : n - half; if ((bits & 1) == 0) offset += n - nextn; n = nextn; } - return offset + nextInt((int)n); + return offset + nextInt((int) n); } /** * Returns a pseudorandom, uniformly distributed value between the * given least value (inclusive) and bound (exclusive). + * * @param least the least value returned * @param bound the upper bound (exclusive) * @return the next value @@ -156,7 +165,8 @@ public class ThreadLocalRandom extends R /** * Returns a pseudorandom, uniformly distributed {@code double} value - * between 0 (inclusive) and the specified value (exclusive) + * between 0 (inclusive) and the specified value (exclusive). + * * @param n the bound on the random number to be returned. Must be * positive. * @return the next value @@ -171,6 +181,7 @@ public class ThreadLocalRandom extends R /** * Returns a pseudorandom, uniformly distributed value between the * given least value (inclusive) and bound (exclusive). + * * @param least the least value returned * @param bound the upper bound (exclusive) * @return the next value @@ -183,4 +194,5 @@ public class ThreadLocalRandom extends R return nextDouble() * (bound - least) + least; } + private static final long serialVersionUID = -5851777807851030925L; }