Java Crash Course: Logic Operators

Logic Operators

Follow along with the instructions at: http://fullstackclouddeveloper.com/course/java-for-beginners/index.html#logic_operators

==

The equality operator returns whether or not the value on the left is equal to the value on the right.

int i = 3;
int j = 2;

boolean b = i == j; // = false

These types of operations are typically used in a conditional statement. We will learn more about conditional statements soon.

int i = 3;
int j = 2;

if (i == j) {
System.out.println("i is equal to j");
}

!=

The inequality operator returns whether or not the value on the left is not equal to the value on the right.

int i = 3;
int j = 2;

if (i != j) {
System.out.println("i is not equal to j");
}

﹤, ﹤=

The less than and less than or equal to operators return whether the value on the left is less than or less than or equal to the value on the right.

int i = 3;
int j = 2;

if (i ﹤= j) {
System.out.println("i is less than or equal to j");
}

﹥, ﹥=

The greater than and greater than or equal to operators return whether the value on the left is greater than or greater than or equal to the value on the right.

int i = 3;
int j = 2;

if (i ﹥= j) {
System.out.println("i is greater than or equal to j");
}

&&

The and operator returns whether or not the condition on the left and the condition on the right are both true.

int i = 3, j = 3, k = 7, l = 5;

if (i == j && k ﹥ l) {
System.out.println("i equals j and k is greater than l");
}

||

The or operator returns whether the condition on the left is true or the condition on the right is true.

int i = 3;
int j = 7;

if (i ﹥ 5 || j ﹤ 10) {
System.out.println("either i is greater than 5 or j is less than 10");
}

!

The ! or sometimes called bang is like adding not to the conditional statement.

For example

int a = 1;
int b = 2;

boolean result = a ﹥ b; // = false

Using ! in front of the conditional statement is like saying, not a ﹥ b.

int a = 1;
int b = 2;

boolean result = !(a ﹥ b); // = true
Operator precedence
&& is evaluated before || unless there are parentheses.

In this example, b == c && c == 5 evaluates to false, then a == d is evaluated which makes the whole condition true so the statement will execute.

int a = 1, b = 2, c = 3, d = 1;

if (a == d || b == c && c == 5) {
System.out.println("This code will execute");
}

When we add parentheses, a == d || b == c evaluates to true, but c == 5 evaluates to false making the whole condition false so the statement will not execute.

int a = 1, b = 2, c = 3, d = 1;

if ((a == d || b == c) && c == 5) {
System.out.println("Now it will not execute");
}