Logic
When writing code in any programming language, you will need to account for situations where you need to decide on a path to take given the value of the variables at that point in time. Your program needs to compare values to each other to decide what code to run next. This is called logic.
Let's look at the comparison operators at our disposal in Java!
Equality Operator
The equality operator is the most basic of comparison operators. If the two values being tested are the same, the result will be true, otherwise, the result will be false.
To use this operator, use two equal signs:
System.out.println(3 == 4);
System.out.println(6 == 6);
System.out.println(43 == 454);
false
true
false
Inequality Operator
The inequality operator is the exact opposite of the equality operator. If the two values being tested are the same, the result will be false. Otherwise, if the values are different, the result will be true.
To use this operator, use an exclamation point, followed by an equal sign.
System.out.println(3 != 4);
System.out.println(6 != 6);
System.out.println(43 != 454);
true
false
true
Greater Than and Less Than Operators
You can check if one value is greater than or less than another using the greater than and less than operators.
This is how you use them:
System.out.println(3 > 4);
System.out.println(6 < 6);
System.out.println(43 < 454);
false
false
true
Or Equal To Operators
In the case where you need to check either that the values are equal or that one is less than/greater than another value, there is a specific operator for just that.
This is how you can use the greater than or equal to operator and the less than or equal to operators:
System.out.println(3 >= 4);
System.out.println(6 <= 6);
System.out.println(43 <= 454);
false
true
true
Conditionals
With the ability to return true or false now, we can now try and act on these values. We can do this by utilizing what are called conditionals.
If
Using if is very simple. If the condition inside is true then the code block will run. If it is false, the code block will not run.
Let's say if you eat 3 burgers or more, you win a competition.
int burgersEaten = 4;
if (burgersEaten >= 3) {
System.out.println("You've won the competition!");
}
You've won the competition!
But watch what happens if you do not eat at least 3 burgers:
int burgersEaten = 2;
if (burgersEaten >= 3) {
System.out.println("You've won the competition!");
}
Nothing was printed. That is because the condition inside the if block resulted in false. The code block was skipped entirely and thus the line to print it never executed.
Else
With the else keyword, you can run block of code if the accompanying if condition returned false.
Let's see how this looks in action:
int burgersEaten = 2;
if (burgersEaten >= 3) {
System.out.println("You've won the competition!");
} else {
System.out.println("You've lost the competition. :(");
}
You've lost the competition. :(
Simply put, the because the first if returned false, the first block of code was skipped, leaving the second block of code to run.
Now what if you wanted to have multiple code paths instead?
Else If
This is where else if comes in to play. These keywords are sandwiched after an if and before the else:
int burgersEaten = 2;
if (burgersEaten >= 3) {
System.out.println("You've won the competition!");
} else if (burgersEaten == 2) {
System.out.println("You almost won the competition!");
} else if (burgersEaten == 1) {
System.out.println("You gave it a good try!");
} else {
System.out.println("You didn't come close. :(");
}
You almost won the competition!
When you use if and else if, the first block of code where the condition is true will run, and the rest will be ignored entirely, so order does matter!
Ternary Operator
The ternary operator is a shorthand way to represent an if/else block. It checks a condition and if true, returns the left side, otherwise it will return the right side.
int number = 45;
boolean isEven = number % 2 == 0 ? true : false;
System.out.println("isEven: " + isEven);
false
Ternary operators are really useful for when you want to condense an entire conditional into a single line.
Switch Statement
You can use a switch statement whenever you want to check for many different possible values of something, and run code if there is a match. They are similar to using else if except they can sometimes be more concise and cleaner.
Let's look at one:
int number = 4;
switch (number) {
case 1:
System.out.println("one");
break;
case 2:
System.out.println("two");
break;
case 3:
System.out.println("three");
break;
case 4:
System.out.println("four");
break;
case 5:
System.out.println("five");
break;
}
four
The basic syntax is simple. You put what you want to switch on after the switch keyword, then you list all your cases below. If there is a match, the code inside will be executed. Once there is a match, the break ensures that once the block of code is run, no more checks are performed.
Logical Operators
So far we have seen how to check a single condition and then do something with the result. In the real world, you will often times need to combine the results of multiple conditions before you can make your decision.
To combine the results of more than one condition, you will need to use a logical operator.
And (&&)
The and operator, will only result in true if both conditions are true:
boolean isCold = true;
boolean hasJacket = true;
if (isCold && hasJacket) {
System.out.println("I will put on my jacket since I am cold!");
}
I will put on my jacket since I am cold!
Since both of the conditions were true, the code block executed.
Or (||)
Sometimes you don't need both conditions to be true and instead are okay with just one of the two being true. This is where the or logical operator comes in to play.
boolean thereAreTacos = true;
boolean thereIsPizza = false;
if (thereAreTacos || thereIsPizza) {
System.out.println("I'm glad there's good food here!");
}
I'm glad there's good food here!
Even though in this case there was no pizza in the house, because there were still tacos, the print statement executed and you were very happy as a result. ❤️🌮🍕
Not (!)
The last logical operator we'll take a look at is the not operator. This is used when you simply want to negate the value of the condition.
Let's look at an example:
boolean thereAreTacos = false;
boolean thereIsPizza = false;
boolean thereIsGoodFood = thereAreTacos || thereIsPizza;
if (!thereIsGoodFood) {
System.out.println("There is no good food here :(");
}
There is no good food here :(
In this case, there were neither tacos nor pizza. That made thereIsGoodFood to be false. However, since we used the not operator to negate it, the entire condition was true and we were able to get the print statement to execute!
