Comparison Operators

Comparison operators allow us to compare two values against one another. A comparison returns a boolean result of either true or false. The table below lists each of the common comparison operators and their usages:

A Basic Comparison

In the following example, we compare two variables x and y. We store the result of this comparison in variable z.

int x = 10;
int y = 8;

boolean z = x > y;
System.out.println(z);

What will get printed to the screen? The above comparison, x > y, is evaluating if 10 is greater than 8. Because 10 is indeed greater than 8, z is assigned a value of true. Thus, true will get printed to the screen.

More Practice with Comparisons

Let's get a little more practice. Take a look at the following code segment below. Pay close attention to each comparison and the operator being used.

// Declare some integer variables to use for practice comparisons below.
int a = 3;
int b = 5;
int c = 2;
int d = 3;

// We store the boolean results of each comparison into boolean variables t-z.
boolean t = a > 0;
boolean u = a == d;
boolean v = d >= b;
boolean w = b > c;
boolean x = a != d;
boolean y = d < = a;
boolean z = 4 < = c;

/* In addition to integers, it is possible to compare other data types too.
   Here we are comparing some of the boolean values computed above (t-z).
   We store the results into new boolean variables. */
boolean boolComparison1 = t == u;
boolean boolComparison2 = t == w;
boolean boolComparison3 = t != u;
boolean boolComparison4 = x != y;

// Print out all the integer comparison results
System.out.println("t = " + t);
System.out.println("u = " + u);
System.out.println("v = " + v);
System.out.println("w = " + w);
System.out.println("x = " + x);
System.out.println("y = " + y);
System.out.println("z = " + z);

// Print out all the boolean comparison results
System.out.println("boolComparison1 = " + boolComparison1);
System.out.println("boolComparison2 = " + boolComparison2);
System.out.println("boolComparison3 = " + boolComparison3);
System.out.println("boolComparison4 = " + boolComparison4);

When we run this code, what boolean values (true or false) will get printed to the screen for variables t through z? What boolean values (true or false) will get printed to the screen for each of the boolComparison variables? See if you can figure it out on your own. The solution is given below.

Solution:

Our program prints out:

t = true
u = true
v = false
w = true
x = false
y = true
z = false
boolComparison1 = true
boolComparison2 = true
boolComparison3 = false
boolComparison4 = true

Comparison Operators in a Program

Suppose we want to write a program which restricts people under a certain height from riding on a roller coaster. For this particular roller coaster, people who are under 4 feet (48 inches) are not allowed on the ride. How would we do this?

int heightInInches = readInt("How tall are you (in inches)? ");
boolean isTallEnough = heightInInches >= 48;
System.out.println("Can ride on the roller coaster: " + isTallEnough);

After getting the potential rider's height in inches, we do a comparison to ensure that they are over 48 inches. The result of this comparison is then printed out.

Pitfalls

A common mistake is using = when you actually want to use ==. = is used for assignment of variables whereas == is used for comparing the equality of two values.

For example, x = 5 stores the value 5 into the variable x. However, x == 5 tests to see if the value 5 is equal to the variable x and then returns either true or false. They are not the same thing!