The Biome Navigator

01 / 15

There are so many street signs that they have grown into a jungle

Steve nailed a road sign at the entrance of the village: Go to the desert to the left, go to the jungle to the right, go to the snowfield and go around again... On the eighth block, the vines have tied him into a "human bookmark." Alex arranges destinations into menus: first looking at the same selection value, then looking for the corresponding label.

switch is good at organizing a fixed list: a number or word, compared with several clear options. Whether the life is lower than 8 requires range judgment, which is still suitable for if; whichever item the destination number equals, it is suitable for switch.

• Why do traditional colon switches often require break?
• How to ensure that the arrow switch will not fall into the next route?
• How to get clear prompts for blank, capital and unknown numbers?

02 / 15

Four parts of traditional switch

switch takes a value to select, case writes a clear label, and default catches unlisted values. The colon type enters from the hit label, and break is responsible for leaving the switch and then continuing to execute the outside code.

String biome = "desert";
switch (biome) {
    case "desert":
        System.out.println("Desert Route");
        break;
    case "jungle":
        System.out.println("Jungle Route");
        break;
    default:
        System.out.println("Routes not listed");
}
System.out.println("End of route check");

Desert Route
End of route check

03 / 15

If break is missed, the mine car will drive past the station.

int station = 2;
switch (station) {
    case 1: System.out.println("Pingyuan Station");
    case 2: System.out.println("Desert Station");
    case 3: System.out.println("Snowfield Station");
    default: System.out.println("Repair station");
}

Desert Station
Snowfield Station
Repair station

It only matches case 2, but executes the following statements all the way from there. This is called penetration. The subsequent case labels will not be reused as condition checks; even the default statement may be executed.

int station = 2;
switch (station) {
    case 1: System.out.println("Pingyuan Station"); break;
    case 2: System.out.println("Desert Station"); break;
    case 3: System.out.println("Snowfield Station"); break;
    default: System.out.println("Repair station");
}

Desert Station

04 / 15

Arrow type: Select a grid to execute it

Use -> after case. After this rule is completed, it will not run through to the next rule, and there is no need to add a break. To do multiple things, put them in a pair of curly braces.

String biome = "jungle";
switch (biome) {
    case "desert" -> System.out.println("Desert Route");
    case "jungle" -> System.out.println("Jungle Route");
    case "snow" -> System.out.println("Snowfield route");
    default -> System.out.println("Unknown route");
}

Jungle Route

int station = 4;
switch (station) {
    case 4 -> {
        System.out.println("Seolwon Station opens");
        System.out.println("View the practice material list");
    }
    default -> System.out.println("Other sites");
}

Seolwon Station opens
View the practice material list

05 / 15

switch expression: return a result

switch can also generate a value and load it into a variable. Each route must produce an appropriate result, without allowing one input to lead to an empty treasure chest. Here default ensures that the menu always has a String result.

String biome = "desert";
String advice = switch (biome) {
    case "desert" -> "Check Desert Route";
    case "jungle" -> "Check Jungle Route";
    case "snow" -> "Check Snowfield Route";
    default -> "Unknown route";
};
System.out.println(advice);

Check Desert Route

String zone = "far";
int ticket = switch (zone) {
    case "near" -> 2;
    case "far" -> 5;
    default -> 0;
};
System.out.println("Practice Fare: " + ticket);

Practice Fare: 5

06 / 15

Multi-sentence rules, use yield to return the value

If there are multiple sentences after the arrow of the expression, wrap them in curly braces, and then use yield to return the result. break means to leave, and yield means to hand the result to the outer switch expression.

String zone = "far";
int ticket = switch (zone) {
    case "near" -> 2;
    case "far" -> {
        System.out.println("Preparing long distance route");
        yield 5;
    }
    default -> 0;
};
System.out.println("Fare=" + ticket);

Preparing long distance route
Fare=5

07 / 15

Clear the ticket first, then find the platform

Players may enter JuNgLe, or they may enter more spaces. First strip, then press Locale.ROOT to convert to lowercase, so that uppercase and lowercase and blank spaces at both ends do not affect the internal commands of the program.

String raw = "  JuNgLe ";
String biome = raw.strip()
        .toLowerCase(java.util.Locale.ROOT);
String advice = switch (biome) {
    case "desert" -> "Desert Route";
    case "jungle" -> "Jungle Route";
    case "snow" -> "Snowfield route";
    case "" -> "No input yet";
    default -> "Unknown route: " + biome;
};
System.out.println(advice);

Jungle Route

default To make the problem clear, don't secretly interpret the misspelled jungel as plain. Input errors and ordinary default suggestions are two different tasks; first explain the default behavior when designing.

08 / 15

Several labels share one rule

The arrow type can use commas to juxtapose multiple fixed tags. In the traditional colon style, you can write several case labels in succession so that they can share the following statements. Don't just move commas into old grammar.

String dimension = "nether";
String level = switch (dimension) {
    case "nether", "end" -> "Practice high-risk routes";
    case "overworld" -> "Practice common routes";
    default -> "Unknown dimensions";
};
System.out.println(level);

Practice high-risk routes

int day = 7;
String plan = switch (day) {
    case 1, 2, 3, 4, 5 -> "After-school programming";
    case 6, 7 -> "Weekend construction";
    default -> "Wrong date";
};
System.out.println(plan);

Weekend construction

09 / 15

Stop sign emergency room

The label must be clear and no competition for position can be made

• If case 2 occurs repeatedly, compilation will fail. Each same label appears only once.
• In the fixed value menu of this lesson, the case label must be a constant; ordinary variable local variables are not constant labels.
• To judge the range of health <= 8, use if; do not stuff the comparison condition into a fixed value case.
• If the String switch expression only lists two words and does not have default, there is no guarantee that every input will have a result.

final int DESERT = 2;
int station = 2;
switch (station) {
    case DESERT -> System.out.println("Desert Station");
    default -> System.out.println("Other stations");
}

Desert Station

10 / 15

Predict first, then run, then explain

String biome = " SNOW ".strip()
        .toLowerCase(java.util.Locale.ROOT);
int boots = switch (biome) {
    case "snow" -> 1;
    default -> 0;
};
System.out.println(boots);

int day = 6;
String plan = switch (day) {
    case 6, 7 -> "Weekend construction";
    case 1, 2, 3, 4, 5 -> "Collection after class";
    default -> "Wrong date";
};
System.out.println(plan);

Check: the first question outputs 1, and after cleaning it is snow; the second question outputs "weekend construction", and 6 hits the first group. Change day to 0, 1, 5, 7, 8 and predict the results before running.

11 / 15

Project Blueprint: Choose one of eight transportation stations

Only apply for one ticket at a time: display the complete menu, read in the number, analyze, select the route, and output the practice material list. There is no loop, and you need to buy a second ticket and run it again.

• A legal number is output to a destination, and other destinations are not allowed.
• 0, 9 and other out-of-bounds integers: report number range error.
• abc, decimal, or large number that does not fit into int: Report an integer input error.
• Entering "3" still selects jungle; 0002 and +5 can be parsed into 2 and 5.

12 / 15

Traffic Station Code: Menu and Destination

Create a new BiomeTransit.java, using JDK 21. Put the codes of this page and the next page into the same file in order; the last switch of this page has not ended yet.

import java.util.Scanner;

public class BiomeTransit {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.println("=== Biome Transportation Station ===");
        System.out.println("1 plain  2 Desert  3 Jungle  4 Yukihara.");
        System.out.println("5 Ocean  6 Swamp  7 Badlands  8 Mushroom Island.");
        System.out.println("Destination number 1 to 8: ");
        String text = in.nextLine().strip();
        try {
            int choice = Integer.parseInt(text);
            String destination = switch (choice) {
                case 1 -> "plain";
                case 2 -> "Desert";
                case 3 -> "Jungle";
                case 4 -> "Yukihara.";
                case 5 -> "Ocean";
                case 6 -> "Swamp";
                case 7 -> "Badlands";
                case 8 -> "Mushroom Island.";
                default -> "";
            };

13 / 15

Traffic Station Code: Verification and Materials

            if (destination.isEmpty()) {
                System.out.println("Number must be within 1 to 8 between");
            } else {
                String supply = switch (choice) {
                    case 2 -> "Water and food";
                    case 3 -> "Scissors and torches";
                    case 4 -> "Leather boots";
                    case 5 -> "Boat.";
                    default -> "Bed and food";
                };
                System.out.println("Destination: " + destination);
                System.out.println("Practice material list: " + supply);
            }
        } catch (NumberFormatException e) {
            System.out.println("Please enter an integer number, for example 3");
        }
    }
}

The second switch only processes numbers that are already legal. Entering 3 should output "Destination: Jungle" and "Practice Supply List: Scissors and Torches" after the full menu.

14 / 15

Normal, boundary, and error acceptance

Use input to prove "one vote, one stop"

• Each of the eight legal numbers is tested once to check the destination and materials.
• Then test the empty string, blanks at both ends, 0002, +5.
• If you run the same number repeatedly, the output should be consistent.
• Deliberately repeat a case label, observe the compilation error, and then recover.

Don't just record "success." Write down the input, prediction, and actual output; if there is an extra next stop, go back and check the break in traditional writing. If all use default, first check whether the value and label are consistent.

15 / 15

Add a diamond to your menu

Wooden Pickaxe Task: Four Tool Instructions

Accept pickaxe, axe, shovel, and hoe, and output the tool usage respectively; unknown words will report an error. First clean up whitespace and case, and test four legal words, the empty string and sword.

Iron Pickaxe Task: Weekly Task List

Read 1 to 7, 1 to 5 share the after-school plan, and 6 and 7 share the weekend plan. 0, 8 and abc check for range or parsing errors respectively. Explain why multiple tags can share the same result.

Diamond Pickaxe Task: Three-dimensional menu plus confirmation

Select overworld, nether, end and then read yes/no. Unknown dimensions or confirmation words will report an error, and only yes will show that the preparation is completed. Test at least 8 groups, covering whitespace, upper and lower case, each dimension and unknown words.

Technical Check: Oracle Java 21 Language Guide, switch expressions and statements.
https://docs.oracle.com/en/java/javase/21/language/switch-expressions-and-statements.html