Java中的switch case等價于if else if語句垂蜗。它用于根據(jù)某些條件執(zhí)行語句解幽。

switch(expression) {
    case value_1 :
       // Statements
       break; // optional
       
    case value_2 :
       // Statements
       break; // optional
       
    // If expression does not match with any of above conditions, 
    // default will be executed 
    default : // Optional
       // Statements
}

我們通過一個示例來理解它烘苹。我們將通過一個integer數(shù)字來打印工作日:

package org.ifelse;

public class SwitchDemo {
    public static void main(String[] args) {
        int dayOfWeek = 5;
        switch (dayOfWeek) {
        case 0:
            System.out.println("Sunday");
            break;
        case 1:
            System.out.println("Monday");
            break;
        case 2:
            System.out.println("Tuesday");
            break;
        case 3:
            System.out.println("Wednesday");
            break;
        case 4:
            System.out.println("Thrusday");
            break;
        case 5:
            System.out.println("Friday");
            break;
        case 6:
            System.out.println("Saturday");
            break;

        // Default is executed when expression does not match with any of above
        // conditions.
        default: // Optional
            System.out.println("Invalid day of week");
        }
    }
}

程序運行后結果顯示如下：

Friday

假如將上面示例中的break移除镣衡，看看會發(fā)生什么：

package org.ifelse;

public class SwitchDemo {
    public static void main(String[] args) {
        int dayOfWeek = 5;
        switch (dayOfWeek) {
        case 0:
            System.out.println("Sunday");
        case 1:
            System.out.println("Monday");
        case 2:
            System.out.println("Tuesday");
        case 3:
            System.out.println("Wednesday");
        case 4:
            System.out.println("Thrusday");
        case 5:
            System.out.println("Friday");
        case 6:
            System.out.println("Saturday");

        // Default is executed when expression does not match with any of above
        // conditions.
        default: // Optional
            System.out.println("Invalid day of week");
        }
    }
}

程序運行結果顯示如下：

Friday
Saturday
Invalid day of week

正如你在上面示例中看到的那樣廊鸥，如果你不使用break語句，它會在條件滿足時執(zhí)行條件后的所有語句磨德。

switch case的string示例：
在Java 7之后的switch表達式中使用String吆视。

package org.ifelse;

public class SwitchDemo {
    public static void main(String[] args) {
        String dayOfWeek = "5";
        switch (dayOfWeek) {
        case "0":
            System.out.println("Sunday");
            break;
        case "1":
            System.out.println("Monday");
            break;
        case "2":
            System.out.println("Tuesday");
            break;
        case "3":
            System.out.println("Wednesday");
            break;
        case "4":
            System.out.println("Thrusday");
            break;
        case "5":
            System.out.println("Friday");
            break;
        case "6":
            System.out.println("Saturday");
            break;

        // Default is executed when expression does not match with any of above
        // conditions.
        default: // Optional
            System.out.println("Invalid day of week");
        }
    }
}

程序運行結果顯示如下：

Friday

switch case在內部使用equals方法比較揩环，所以case語句在這里區(qū)分大小寫幅虑。

在switch case和if else if之間進行選擇取決于可讀性和各種因素。你可以根據(jù)自己的需要進行選擇褒墨。