How do I use the equality operator in Java?

By Wayan in Basic, Core API 0 Comment

Equality operator is used to compare two similar things (numbers, characters, boolean, primitives and object references). Equality operator will always result in boolean value (true or false).

For object reference, it will return true if only both reference variables refer to the same object.

package org.kodejava.basic;

public class EqualityDemo {
    public static void main(String[] args) {
        int value1 = 10, value2 = 10, number1 = 10;
        char a = 'a', b = 'b';
        double number2 = 10d;
        Cat kitty = new Cat("Kitty");
        Cat kitten = new Cat("Kitty");
        Cat sweetie = kitty;

        if (value1 == value2) {
            System.out.println("Equal");
        }

        if (a != b) {
            System.out.println("Not Equal");
        }

        // though it have different type, but it have same value
        if (number1 == number2) {
            System.out.println("Equal");
        }

        // it's not refer to the same object, so it will return
        // false
        if (kitty == kitten) {
            System.out.format("(kitty == kitten) = " + (kitty == kitten));
        } else {
            System.out.println("(kitty == kitten) = " + (kitty == kitten));
        }

        // it's refer to the same object, so it will return true
        if (kitty == sweetie) {
            System.out.println("(kitty == sweetie) = " + (kitty == sweetie));
        }

        if (true != false) {
            System.out.println("true != false");
        }

    }
}

class Cat {
    private String name;

    Cat(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

And here are the result of the program:

Equal
Not Equal
Equal
(kitty == kitten) = false
(kitty == sweetie) = true
true != false

How do I use the && operator in Java?

By Wayan in Basic, Core API 0 Comment

The && operator also known as conditional-AND operator or short circuit AND. This operator exhibit “short-circuiting” behavior, which means that the second operand is evaluated only if needed.

The && operator evaluate only boolean values. For an AND (&&) expression to be true, both operands must be true. If the first operand resolves false, then the && operator will not evaluate the second operand, because it already know the complete expression will return false.

package org.kodejava.basic;

public class ConditionalANDDemo {
    public static void main(String[] args) {
        // second operand (2<3) is not evaluated, because the first
        // operand return false the result of complete expression
        // can't be true
        boolean a = (5 < 3) && (2 < 3);

        // first operand return true, second operand is evaluated
        // to check the result of the second expression if second
        // operand resolves to true, the complete expression return
        // false, otherwise return false
        boolean b = (1 == 1) && (2 < 3);
        boolean c = (1 == 1) && (5 < 3);

        System.out.println("result a: " + a);
        System.out.println("result b: " + b);
        System.out.println("result c: " + c);
    }
}

The result of the code snippet:

result a: false
result b: true
result c: false

How do I define a constant variable?

By Wayan in Basic, Core API 0 Comment

To define a constant in Java, use final modifier which combined with static modifier. The final modifier indicates that the value of this field cannot change.

If you change the value of the constant, you need to recompile the class to get the current value. Other feature in Java that provide similar functionality is enumeration (a list of named constants). You can simply create an enumeration by using the enum keyword.

package org.kodejava.example.fundamental;

public class ConstantDemo {
    public static void main(String[] args) {
        int sunday = DayConstant.SUNDAY;
        System.out.println("Sunday = " + sunday);

        String dozen = MeasureConstant.DOZEN;
        System.out.println("Dozen  = " + dozen);
    }
}

class DayConstant {
    public final static int SUNDAY = 0;
    public final static int MONDAY = 1;
    public final static int TUESDAY = 2;
    public final static int WEDNESDAY = 3;
    public final static int THURSDAY = 4;
    public final static int FRIDAY = 5;
    public final static int SATURDAY = 6;
}

class MeasureConstant {
    final static String UNIT = "unit";
    final static String DOZEN = "dozen";
}

How do I calculate the length of hypotenuse?

By Wayan in Core API, Math 0 Comment

Hypot is a mathematical function defined to calculate the length of the hypotenuse of a right-angle triangle. It was designed to avoid errors arising due to limited-precision calculations performed on computers.

From: Wikipedia

The Math.hypot(double x, double y) return the sqrt(x2+ y2) without intermediate overflow or underflow. The result will be same with this calculation Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2)).

package org.kodejava.math;

public class HypotExample {
    public static void main(String[] args) {
        double number1 = 3.0d;
        double number2 = 5.0d;

        // calculate square root of total value of
        // number1 ^ 2 + number2 ^ 2
        double sqr = Math.hypot(number1, number2);

        System.out.println("Total value = " +
                (Math.pow(number1, 2) + Math.pow(number2, 2)));
        System.out.println("Square root = " + sqr);
    }
}

How do I calculate exponential function?

By Wayan in Core API, Math 1 Comment

In mathematics, the exponential function is the function ex, where e is the number (approximately 2.718281828) such that the function ex equals its own derivative. The function f(x) = ex at the point x = 0 is equal to 1.

package org.kodejava.math;

public class ExponentExample {

    public static void main(String[] args) {
        double x = 0.0d;

        // calculates e raised to the power of x (e^x)
        double fx = Math.exp(x);

        // calculates e raised to the power of x minus 1 (e^x - 1)
        double fxm1 = Math.expm1(x);

        System.out.println("fx   = " + fx);
        System.out.println("fxm1 = " + fxm1);
    }
}