In Java, the boolean data type is used to represent two values: true or false. Booleans are often used in control flow statements like if, while, and logical operations, where you need to check if a condition is either true or false.
- Declaring Boolean Variables
To declare a boolean variable in Java, use the boolean keyword. The value of the boolean can either be true or false.
Example:
public class Main {
public static void main(String[] args) {
boolean isJavaFun = true;
boolean isFishTasty = false;
System.out.println(“Is Java fun? ” + isJavaFun); // Outputs true
System.out.println(“Is fish tasty? ” + isFishTasty); // Outputs false
}
}
- Boolean Expressions
A Boolean expression is an expression that evaluates to either true or false. These expressions typically involve comparison or logical operations.
Comparison Operators
You can create Boolean expressions by using comparison operators such as:
- == (equal to)
- != (not equal to)
- > (greater than)
- < (less than)
- >= (greater than or equal to)
- <= (less than or equal to)
Example:
java
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public class Main {
public static void main(String[] args) {
int x = 10;
int y = 20;
System.out.println(x > y); // Outputs false
System.out.println(x < y); // Outputs true
System.out.println(x == 10); // Outputs true
}
}
Logical Operators
Java also provides logical operators to combine multiple Boolean expressions:
- && (logical AND): Returns true if both expressions are true.
- || (logical OR): Returns true if at least one of the expressions is true.
- ! (logical NOT): Reverses the Boolean value (true becomes false, and false becomes true).
Example:
public class Main {
public static void main(String[] args) {
int x = 10;
int y = 20;
// Logical AND (both conditions must be true)
System.out.println(x > 5 && y > 15); // Outputs true
// Logical OR (at least one condition must be true)
System.out.println(x < 5 || y > 15); // Outputs true
// Logical NOT (reverses the result)
System.out.println(!(x > 5)); // Outputs false
}
}
- Booleans in Conditional Statements
Boolean values are most commonly used in conditional statements, such as if-else and loops (while, for). These statements execute code based on whether a condition is true or false.
Example: if-else Statement
public class Main {
public static void main(String[] args) {
boolean isRaining = false;
if (isRaining) {
System.out.println(“Take an umbrella!”);
} else {
System.out.println(“Enjoy the sunshine!”);
}
}
}
In this example:
- If isRaining is true, it will print “Take an umbrella!”.
- Otherwise, it will print “Enjoy the sunshine!”.
- Boolean Return Values
Boolean values are often returned from methods that check a condition or validate data. These methods usually return true or false based on some logic.
Example: Method Returning a Boolean
public class Main {
public static void main(String[] args) {
System.out.println(isEven(10)); // Outputs true
System.out.println(isEven(7)); // Outputs false
}
// Method to check if a number is even
public static boolean isEven(int number) {
return number % 2 == 0;
}
}
In this example, the isEven() method returns true if the number is even and false if it’s odd.
- Boolean Default Value
In Java, when a boolean variable is declared as an instance variable (i.e., outside of a method but inside a class), its default value is false.
Example:
public class Main {
static boolean myBoolean; // Default value is false
public static void main(String[] args) {
System.out.println(myBoolean); // Outputs false
}
}
- Boolean Wrapping Class
In addition to the primitive boolean type, Java provides a wrapper class for booleans called Boolean. This is useful when you need to work with objects instead of primitive types, such as when storing Boolean values in collections like ArrayList.
Example:
public class Main {
public static void main(String[] args) {
Boolean isJavaAwesome = Boolean.TRUE;
Boolean isDifficult = Boolean.FALSE;
System.out.println(“Java is awesome: ” + isJavaAwesome); // Outputs true
System.out.println(“Java is difficult: ” + isDifficult); // Outputs false
}
}
The Boolean class also provides methods to convert strings to boolean values and vice versa:
- Boolean.parseBoolean(String): Converts a string to a boolean (“true” returns true, any other string returns false).
- Boolean.toString(boolean): Converts a boolean value to its string representation.
Example:
public class Main {
public static void main(String[] args) {
String boolStr = “true”;
boolean boolValue = Boolean.parseBoolean(boolStr);
System.out.println(boolValue); // Outputs true
}
}
Summary
Booleans are a fundamental data type in Java that represent true or false values. They are essential for making decisions in code using conditional statements like if, while, and for. Java also provides logical operators and a Boolean wrapper class for more advanced manipulations of boolean values.