public Builder<G, C> survivorsSize(final int size) {
			if (size < 0) {
				throw new IllegalArgumentException(format(
					"Survivors must be greater or equal zero, but was %s.",
					size
				));
			}

			return survivorsFraction(size/(double)_evolutionParams.populationSize());
		}
The number of survivors.

@since 3.8

@param size the number of survivors.
@return {@code this} builder, for command chaining
@throws java.lang.IllegalArgumentException if the size is not
        within the range [0, population-size].
jenetics/src/main/java/io/jenetics/engine/Engine.java