Night Falls: if or else?

Complete program: Save as HealthAlert.java

public class HealthAlert {
    public static void main(String[] args) {
        int health = 7;
        if (health <= 8) {
            System.out.println("Supply first");
        }
        System.out.println("End of inspection");
    }
}

Output

Supply first
End of inspection

Snippet: place inside main and run separately

boolean isNight = true;
if (isNight) {
    System.out.println("Return to the house to rest");
} else {
    System.out.println("Collection during the day");
}

Output

Return to the house to rest

Snippet: place inside main and run separately

int diamonds = 2;
if (diamonds >= 3) {
    System.out.println("The number of diamonds is enough");
} else {
    System.out.println("Not much." + (3 - diamonds) + "diamonds");
}

Output

Not much.1diamonds

Snippet: place inside main and run separately

int health = 7;
if (health <= 0) {
    System.out.println("Reborn.");
} else if (health <= 8) {
    System.out.println("Eat something quickly");
} else {
    System.out.println("Continue the adventure");
}

Output

Eat something quickly

Snippet: place inside main and run separately

boolean isNight = true, hasShelter = false;
if (isNight && !hasShelter) {
    System.out.println("Build temporary shelter first");
}

Output

Build temporary shelter first

Snippet: place inside main and run separately

boolean hasKey = false, isOwner = true;
if (hasKey || isOwner) {
    System.out.println("The door is open");
}

Output

The door is open

Snippet: place inside main and run separately

String weather = " RAIN ".strip();
if ("rain".equalsIgnoreCase(weather)) {
    System.out.println("Move the construction plan indoors");
}

Output

Move the construction plan indoors

Snippet: place inside main and run separately

int health = 6;
if (health <= 8) {
    System.out.println("Bring bread");
}
if (health <= 16) {
    System.out.println("With shield");
}

Output

Bring bread
With shield

Snippet: place inside main and run separately

int health = 6;
if (health <= 8) {
    System.out.println("Bring bread");
} else if (health <= 16) {
    System.out.println("With shield");
}

Output

Bring bread

Snippet: place inside main and run separately

int health = 8;
if (health < 0 || health > 20) {
    System.out.println("Life range error");
} else if (health == 0) {
    System.out.println("Reborn.");
} else if (health <= 8) {
    System.out.println("Low life");
} else if (health <= 16) {
    System.out.println("Proceed with caution");
} else {
    System.out.println("Sufficient life");
}

Output

Low life

Snippet: place inside main and run separately

boolean isNight = true, hasShelter = false;
if (isNight) {
    if (hasShelter) {
        System.out.println("Return to the house to rest");
    } else {
        System.out.println("Build temporary shelter first");
    }
} else {
    System.out.println("Collection during the day");
}

Output

Build temporary shelter first

Snippet: place inside main and run separately

boolean isNight = false;
String advice;
if (isNight) {
    advice = "Go home";
} else {
    advice = "Collection";
}
System.out.println(advice);

Output

Collection

Logical counterexample: predict first, then find redundant symbols

boolean isNight = false;
if (isNight); { // Error demonstration: extra semicolons
    System.out.println("Close the door");
}

Output

Close the door

Logical counterexample: the key was secretly changed by the program

boolean hasKey = false;
if (hasKey = true) { // Error demonstration: assignment, not comparison
    System.out.println("Open the door");
}

Output

Open the door

Snippet: place inside main and run separately

int diamonds = 3, sticks = 1;
if (diamonds >= 3 && sticks >= 2) {
    System.out.println("The materials are ready");
} else {
    System.out.println("The materials are not yet complete");
}

Snippet: place inside main and run separately

int health = 8;
if (health <= 8) {
    health += 2;
}
if (health > 8) {
    health += 1;
}
System.out.println(health);

NightAdvisor.java · First half, continue on next page

import java.util.Scanner;

public class NightAdvisor {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.println("Life 0-20: ");
        String healthText = in.nextLine().strip();
        System.out.println("Period day/night: ");
        String time = in.nextLine().strip();
        System.out.println("Have a place to live yes/no: ");
        String home = in.nextLine().strip();
        boolean timeOK = "day".equalsIgnoreCase(time)
                || "night".equalsIgnoreCase(time);
        boolean homeOK = "yes".equalsIgnoreCase(home)
                || "no".equalsIgnoreCase(home);
        if (!timeOK || !homeOK) {
            System.out.println("The option is wrong, please check the time period and residence");
        } else {
            try {
                int health = Integer.parseInt(healthText);
                boolean isNight = "night".equalsIgnoreCase(time);
                boolean hasShelter = "yes".equalsIgnoreCase(home);

NightAdvisor.java · Next to the previous page

                if (health < 0 || health > 20) {
                    System.out.println("Life must be 0 to 20 between");
                } else if (health == 0) {
                    System.out.println("Life is exhausted, prepare for rebirth");
                } else if (health <= 8) {
                    System.out.println("Go to a safe place for supplies first");
                } else if (isNight) {
                    if (hasShelter) {
                        System.out.println("Return to the house to rest");
                    } else {
                        System.out.println("Build temporary shelter first");
                    }
                } else {
                    System.out.println("Collect during the day, don’t forget to bring supplies");
                }
            } catch (NumberFormatException e) {
                System.out.println("Please enter life 0 to 20 integer");
            }
        }
    }
}