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Random.NextInt Method

  • Reference

Definition

Namespace:
Java.Util
Assembly:
Mono.Android.dll

Overloads

NextInt()

Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence.
NextInt(Int32)

Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.

NextInt()

Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence.

[Android.Runtime.Register("nextInt", "()I", "GetNextIntHandler")]
public virtual int NextInt ();
[<Android.Runtime.Register("nextInt", "()I", "GetNextIntHandler")>]
abstract member NextInt : unit -> int
override this.NextInt : unit -> int

Returns

Int32

the next pseudorandom, uniformly distributed int value from this random number generator's sequence

Attributes
RegisterAttribute

Remarks

Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence. The general contract of nextInt is that one int value is pseudorandomly generated and returned. All 2<sup>32</sup> possible int values are produced with (approximately) equal probability.

The method nextInt is implemented by class Random as if by:

{@code
            public int nextInt() {
              return next(32);
            }}

Java documentation for java.util.Random.nextInt().

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.

Applies to

NextInt(Int32)

Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.

[Android.Runtime.Register("nextInt", "(I)I", "GetNextInt_IHandler")]
public virtual int NextInt (int bound);
[<Android.Runtime.Register("nextInt", "(I)I", "GetNextInt_IHandler")>]
abstract member NextInt : int -> int
override this.NextInt : int -> int

Parameters

bound
Int32

the upper bound (exclusive). Must be positive.

Returns

Int32

the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence

Attributes
RegisterAttribute

Remarks

Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract of nextInt is that one int value in the specified range is pseudorandomly generated and returned. All bound possible int values are produced with (approximately) equal probability. The method nextInt(int bound) is implemented by class Random as if by:

{@code
            public int nextInt(int bound) {
              if (bound <= 0)
                throw new IllegalArgumentException("bound must be positive");

              if ((bound & -bound) == bound)  // i.e., bound is a power of 2
                return (int)((bound * (long)next(31)) >> 31);

              int bits, val;
              do {
                  bits = next(31);
                  val = bits % bound;
              } while (bits - val + (bound-1) < 0);
              return val;
            }}

The hedge "approximately" is used in the foregoing description only because the next method is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm shown would choose int values from the stated range with perfect uniformity.

The algorithm is slightly tricky. It rejects values that would result in an uneven distribution (due to the fact that 2^31 is not divisible by n). The probability of a value being rejected depends on n. The worst case is n=2^30+1, for which the probability of a reject is 1/2, and the expected number of iterations before the loop terminates is 2.

The algorithm treats the case where n is a power of two specially: it returns the correct number of high-order bits from the underlying pseudo-random number generator. In the absence of special treatment, the correct number of low-order bits would be returned. Linear congruential pseudo-random number generators such as the one implemented by this class are known to have short periods in the sequence of values of their low-order bits. Thus, this special case greatly increases the length of the sequence of values returned by successive calls to this method if n is a small power of two.

Added in 1.2.

Java documentation for java.util.Random.nextInt(int).

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.

Applies to