The switch-case construct in Java is a flow control structure designed to evaluate the value of a variable against a list of predefined values. The syntax for this structure is as follows:

switch (expression) {
    case constant_1:
        // statement 1
        break;
    case constant_2:
        // statement 2
        break;
    case constant_3:
        // statement 3
        break;
    //...
    case constant_n:
        // statement n
        break;
    default:
        // if none of the cases match
}

Here are some rules regarding the switch-case construct:

• The expression is a variable or an expression that must evaluate to one of the following types: primitive numbers (byte, short, char, int), primitive wrappers (Byte, Short, Character, Integer), enumerated types (enum type), and string literals (since Java 1.7).
• The constants (constant_1, constant_2, ..., constant_n) must be literals or constants of the allowed types.
• Each case is tested from top to bottom until a case is matched, and then the corresponding block of statements is executed until a break statement is encountered.
• It's not mandatory for each case to have a break statement. If a matching case block lacks a break statement, execution will continue to the next case block until a break statement is encountered or the end of the switch statement is reached.
• The statements block after the default case will be executed if no matching case is found.

Let's explore some examples of switch-case in Java:

Example 1:

int number = 3;
String text = "";

switch (number) {
    case 1:
        text = "One";
        break;
    case 2:
        text = "Two";
        break;
    case 3:
        text = "Three";
        break;
    default:
        text = "Other number";
}

System.out.println("The number is: " + text);

Example 2:

String planet = "Jupiter";
long distanceFromEarth = 0;

switch (planet) {
    case "Mars":
        distanceFromEarth = 3;
        break;
    case "Saturn":
        distanceFromEarth = 5;
        break;
    case "Jupiter":
        distanceFromEarth = 4;
        break;
    case "Venus":
        distanceFromEarth = 1;
        break;
}

System.out.println("The distance from earth to " + planet + " is: " + distanceFromEarth);

Example 3:

Priority priority = Priority.HIGH;
int taskPriority = 0;

switch (priority) {
    case LOW:
        taskPriority = 1;
        break;
    case NORMAL:
        taskPriority = 2;
        break;
    case HIGH:
        taskPriority = 3;
        break;
    case SEVERE:
        taskPriority = 4;
        break;
}

System.out.println("Task priority: " + taskPriority);

The enum Priority is declared as follows:

public enum Priority { LOW, NORMAL, HIGH, SEVERE }

Starting from Java 14, you can use the switch block as an expression:

int taskPriority = switch (priority) {
    case LOW -> 1;
    case NORMAL -> 2;
    case HIGH -> 3;
    case SEVERE -> 4;
};

System.out.println("Task priority: " + taskPriority);