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L1

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Assertions1.java
import org.pureprogrammer.Utils;

public class Assertions1 {

	static final double TEST_BASE = 0.9;

	static double exponentiation(double base, int powerArg) {
		assert powerArg >= 0 : "powerArg >= 0";
		int power = powerArg;
		double result = 1.0;
		while (power > 0) {
			result *= base;
			--power;
		}
		return result;
	}

	public static void main(String[] args) {
		for (int p = 10; p >= -1; --p) {
			System.out.println(Utils.format("{0:f} ^ {1:d} = {2:f}", TEST_BASE, p, exponentiation(TEST_BASE, p)));
		}
	}
}
Output
$ javac -Xlint Assertions1.java $ java -ea Assertions1 0.900000 ^ 10 = 0.348678 0.900000 ^ 9 = 0.387420 0.900000 ^ 8 = 0.430467 0.900000 ^ 7 = 0.478297 0.900000 ^ 6 = 0.531441 0.900000 ^ 5 = 0.590490 0.900000 ^ 4 = 0.656100 0.900000 ^ 3 = 0.729000 0.900000 ^ 2 = 0.810000 0.900000 ^ 1 = 0.900000 0.900000 ^ 0 = 1.000000 Exception in thread "main" java.lang.AssertionError: powerArg >= 0 at Assertions1.exponentiation(Assertions1.java:8) at Assertions1.main(Assertions1.java:20)
Assertions2.java
import org.pureprogrammer.Utils;

public class Assertions2 {

	static final double TEST_BASE = 0.9;

	static double exponentiation(double base, int powerArg) {
		assert powerArg >= 0 : Utils.join("", "exponentiation() power must be non-negative, was ", powerArg);
		int power = powerArg;
		double result = 1.0;
		while (power > 0) {
			result *= base;
			--power;
		}
		return result;
	}

	public static void main(String[] args) {
		for (int p = 10; p >= -1; --p) {
			System.out.println(Utils.format("{0:f} ^ {1:d} = {2:f}", TEST_BASE, p, exponentiation(TEST_BASE, p)));
		}
	}
}
Output
$ javac -Xlint Assertions2.java $ java -ea Assertions2 0.900000 ^ 10 = 0.348678 0.900000 ^ 9 = 0.387420 0.900000 ^ 8 = 0.430467 0.900000 ^ 7 = 0.478297 0.900000 ^ 6 = 0.531441 0.900000 ^ 5 = 0.590490 0.900000 ^ 4 = 0.656100 0.900000 ^ 3 = 0.729000 0.900000 ^ 2 = 0.810000 0.900000 ^ 1 = 0.900000 0.900000 ^ 0 = 1.000000 Exception in thread "main" java.lang.AssertionError: exponentiation() power must be non-negative, was -1 at Assertions2.exponentiation(Assertions2.java:8) at Assertions2.main(Assertions2.java:20)
Assertions3.java
import org.pureprogrammer.Utils;

public class Assertions3 {

	static final double TEST_BASE = 0.9;

	static double exponentiation(double base, int powerArg) {
		assert powerArg >= 0 : Utils.join("", "exponentiation() power must be non-negative, was ", powerArg);
		int power = powerArg;
		double result = 1.0;
		while (power > 0) {
			result *= base;
			--power;
		}
// This line will make the result incorrect.
		result = -result;
// If power is odd and base is negative, then result should be negative.
// Otherwise result should be positive.
		assert (power & 1) == 1 && (base < 0.0) ? result < 0.0 : result >= 0.0 : "Postcondition Failed: Result is wrong sign";
		return result;
	}

	public static void main(String[] args) {
		for (int p = 10; p >= -1; --p) {
			System.out.println(Utils.format("{0:f} ^ {1:d} = {2:f}", TEST_BASE, p, exponentiation(TEST_BASE, p)));
		}
	}
}
Output
$ javac -Xlint Assertions3.java $ java -ea Assertions3 Exception in thread "main" java.lang.AssertionError: Postcondition Failed: Result is wrong sign at Assertions3.exponentiation(Assertions3.java:19) at Assertions3.main(Assertions3.java:25)
java

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