Dear students,
We have seen the Computer as Calculator, a lover of number crunching. We have seen the Computer as Chef, organizing its tasks into self-contained recipes. Now we see the Computer as Philosopher, seeking truth from our data.
Truth is communicated in our programs through the boolean
data type. Values of type boolean
can only be true
or false
. We’ve already seen some ways to generate such values: String.startsWith
, String.endsWith
, String.contains
, String.isEmpty
, Random.nextBoolean
, and so on. There are also a number of operators that yield boolean
truths, and these are our focus for today.
To begin, let’s meet the relational operators: <
, <=
, >
, >=
, ==
, and !=
. ==
and !=
are sometimes distinguished as equality operators. We’ll introduce these by writing some methods that serve as predicates, answering yes/no questions like these:
"logout"
?
String
able to be converted to an int
?
Here’s your TODO list to complete before our next lecture:
&&
, ||
, and !
. For example, here’s one that may or may not apply to you: boolean isEdible = isCooked || !isMeat;
See you next class!
P.S. It’s time for a haiku!
i <3 u
ur at least a third of me
better half, likely
P.P.S. Here’s the code we wrote together in class…
package lecture1004.cs145;
public class Certainly {
public static void samesies(int expected, int actual) {
System.out.printf("%d == %d%n", expected, actual);
}
public static void samesies(boolean expected, boolean actual) {
System.out.printf("%b == %b%n", expected, actual);
}
}
package lecture1004.cs145;
public class Booleandrews {
public static void main(String[] args) {
Certainly.samesies(false, isSocialSecurityEligible(14));
Certainly.samesies(true, isSocialSecurityEligible(74));
Certainly.samesies(true, isSocialSecurityEligible(62));
Certainly.samesies(false, isSocialSecurityEligible(61));
Certainly.samesies(false, isWalk(0, false));
Certainly.samesies(true, isWalk(4, false));
Certainly.samesies(false, isWalk(3, false));
Certainly.samesies(false, isPolygamous(0));
Certainly.samesies(false, isPolygamous(1));
Certainly.samesies(true, isPolygamous(2));
Certainly.samesies(true, isPolygamous(17));
Certainly.samesies(true, isLegalToDrive(0));
Certainly.samesies(true, isLegalToDrive(0.0799999));
Certainly.samesies(false, isLegalToDrive(0.08));
Certainly.samesies(false, isLegalToDrive(0.09));
Certainly.samesies(false, isLegalToDrive(2));
Certainly.samesies(true, isWrongNumber(11, 7));
Certainly.samesies(false, isWrongNumber(11, 11));
Certainly.samesies(false, isWrongNumber(0.001, 0.001));
Certainly.samesies(false, isWrongNumber(0.001, 0.0005 + 0.0005));
Certainly.samesies(true, isWrongNumber(0.001, 0.0004 + 0.0005));
Certainly.samesies(false, isWrongNumber(0.001, 0.0010));
Certainly.samesies(true, isNameTattooable(10, "Chris"));
Certainly.samesies(false, isNameTattooable(10, "Christopher"));
Certainly.samesies(false, isNameTattooable(10, "Demosthenes"));
Certainly.samesies(false, isNameTattooable(0, "Mom"));
Certainly.samesies(true, isNameTattooable(0, ""));
}
public static boolean isSocialSecurityEligible(int age) {
return age >= 62;
}
public static boolean isWalk(int numberOfBalls, boolean isHitByPitch) {
return numberOfBalls == 4;
}
public static boolean isPolygamous(int nSpouses) {
return nSpouses > 1;
}
public static boolean isLegalToDrive(double bac) {
return bac < 0.08;
}
public static boolean isWrongNumber(double rightNumber, double guess) {
// return rightNumber != guess;
return Math.abs(rightNumber - guess) > 0.001;
}
public static boolean isNameTattooable(int nKnuckles, String name) {
return nKnuckles >= name.length();
}
}
package lecture1004.cs148;
public class Quarter {
public static boolean hasJustOne(String haystack, char needle) {
int count = haystack.length() - haystack.replaceAll("" + needle, "").length();
return count == 1;
}
public static boolean hasJustOneJustin(String haystack, char needle) {
return haystack.indexOf(needle) == haystack.lastIndexOf(needle);
}
public static boolean hasJustOneVictor(String haystack, char needle) {
int count = 0;
for (int i = 0; i < haystack.length(); ++i) {
if (haystack.charAt(i) == needle) {
return true;
}
}
return count == 1;
}
}
package lecture1004.cs148;
public class Certainly {
public static void samesies(int expected, int actual, String message) {
if (expected != actual) {
throw new RuntimeException(String.format("%s%nExpected: %d%n Actual: %d%n", message, expected, actual));
}
}
public static void samesies(boolean expected, boolean actual, String message) {
if (expected != actual) {
throw new RuntimeException(String.format("%s%nExpected: %b%n Actual: %b%n", message, expected, actual));
}
}
}
package lecture1004.cs148;
public class Booleanning {
public static void main(String[] args) {
Certainly.samesies(false, isSocialSecurityEligible(25), "");
Certainly.samesies(true, isSocialSecurityEligible(65), "");
Certainly.samesies(false, isSocialSecurityEligible(18), "");
Certainly.samesies(true, isSocialSecurityEligible(300), "");
Certainly.samesies(true, isSocialSecurityEligible(62), "");
Certainly.samesies(false, isSocialSecurityEligible(61), "");
Certainly.samesies(false, isWalk(0), "walk 0");
Certainly.samesies(false, isWalk(1), "walk 1");
Certainly.samesies(false, isWalk(2), "walk 2");
Certainly.samesies(false, isWalk(3), "walk 3");
Certainly.samesies(true, isWalk(4), "walk 4");
Certainly.samesies(false, isPolygamous(0), "poly 0");
Certainly.samesies(false, isPolygamous(1), "poly 1");
Certainly.samesies(true, isPolygamous(2), "poly 2");
Certainly.samesies(true, isPolygamous(17), "poly 17");
Certainly.samesies(true, isLegalToDrive(0), "bac 0");
Certainly.samesies(true, isLegalToDrive(0.079999), "bac 0.079999");
Certainly.samesies(false, isLegalToDrive(0.08), "bac 0.08");
Certainly.samesies(false, isLegalToDrive(0.09), "bac 0.09");
Certainly.samesies(true, isTattooable(10, "Sam"), "sam");
Certainly.samesies(false, isTattooable(10, "Bartholomew"), "Barthomolew");
Certainly.samesies(false, isTattooable(10, "Demosthenes"), "Demosthenes");
}
public static boolean isSocialSecurityEligible(int age) {
return age >= 62;
}
public static boolean isWalk(int nBalls) {
return nBalls == 4;
}
public static boolean isPolygamous(int nPartners) {
return nPartners >= 2;
}
public static boolean isLegalToDrive(double bac) {
return bac < 0.08;
}
public static boolean isTattooable(int nKnuckles, String name) {
int nCharacters = name.length();
return nKnuckles >= nCharacters;
}
}
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