在我的代码中,程序根据用户输入的文本执行某些操作。
switch (name) {
case text1: {
//blah
break;
}
case text2: {
//blah
break;
}
case text3: {
//blah
break;
}
case text4: {
//blah
break;
}
但是,casestext1
和text4
中的代码是相同的。因此,我想知道是否有可能实现类似
case text1||text4: {
//blah
break;
}
我知道||
运算符在 case 语句中不起作用,但是有类似的东西我可以使用。
您可以使用两个CASE
语句,如下所示。
case text1:
case text4:{
//blah
break;
}
请参阅此示例:代码示例计算特定月份的天数:
class SwitchDemo {
public static void main(String[] args) {
int month = 2;
int year = 2000;
int numDays = 0;
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
numDays = 31;
break;
case 4:
case 6:
case 9:
case 11:
numDays = 30;
break;
case 2:
if (((year % 4 == 0) &&
!(year % 100 == 0))
|| (year % 400 == 0))
numDays = 29;
else
numDays = 28;
break;
default:
System.out.println("Invalid month.");
break;
}
System.out.println("Number of Days = "
+ numDays);
}
}
这是代码的输出:
Number of Days = 29
FALLTHOUGH:
另一个关注点是 break 语句。每个 break 语句终止封闭的 switch 语句。控制流继续 switch 块后面的第一个语句。break 语句是必需的,因为没有它们,switch 块中的语句fall through
:匹配 case 标签之后的所有语句都将按顺序执行,而不管后续 case 标签的表达式如何,直到遇到 break 语句。
示例代码:
public class SwitchFallThrough {
public static void main(String[] args) {
java.util.ArrayList<String> futureMonths =
new java.util.ArrayList<String>();
int month = 8;
switch (month) {
case 1: futureMonths.add("January");
case 2: futureMonths.add("February");
case 3: futureMonths.add("March");
case 4: futureMonths.add("April");
case 5: futureMonths.add("May");
case 6: futureMonths.add("June");
case 7: futureMonths.add("July");
case 8: futureMonths.add("August");
case 9: futureMonths.add("September");
case 10: futureMonths.add("October");
case 11: futureMonths.add("November");
case 12: futureMonths.add("December");
default: break;
}
if (futureMonths.isEmpty()) {
System.out.println("Invalid month number");
} else {
for (String monthName : futureMonths) {
System.out.println(monthName);
}
}
}
}
这是代码的输出:
August
September
October
November
December
在 switch 语句中使用字符串
在 Java SE 7 及更高版本中,可以在 switch 语句的表达式中使用 String 对象。的代码示例根据名为 month 的 String 的值显示月份数:
public class StringSwitchDemo {
public static int getMonthNumber(String month) {
int monthNumber = 0;
if (month == null) {
return monthNumber;
}
switch (month.toLowerCase()) {
case "january":
monthNumber = 1;
break;
case "february":
monthNumber = 2;
break;
case "march":
monthNumber = 3;
break;
case "april":
monthNumber = 4;
break;
case "may":
monthNumber = 5;
break;
case "june":
monthNumber = 6;
break;
case "july":
monthNumber = 7;
break;
case "august":
monthNumber = 8;
break;
case "september":
monthNumber = 9;
break;
case "october":
monthNumber = 10;
break;
case "november":
monthNumber = 11;
break;
case "december":
monthNumber = 12;
break;
default:
monthNumber = 0;
break;
}
return monthNumber;
}
public static void main(String[] args) {
String month = "August";
int returnedMonthNumber =
StringSwitchDemo.getMonthNumber(month);
if (returnedMonthNumber == 0) {
System.out.println("Invalid month");
} else {
System.out.println(returnedMonthNumber);
}
}
}
此代码的输出为 8。
FROM Java Docs您可以执行以下操作,为一个 switch 语句使用多个 case:
case "firstCase":
case "secondCase": {
// Run code here for both cases
}
case
值只是可以共享相同入口点的无代码“goto”点:
case text1:
case text4:
//blah
break;
请注意,大括号是多余的。
摘要:用逗号分隔
switch (name) {
case text1 , text4 -> doX() ;
case text2 -> doY() ;
case text3 -> doZ() ;
}
开关表达式
通过在Java 14和更高版本中集成JEP 361: Switch Expressions,可以使用在多个值之间使用逗号的开关标签的新形式。
case text1, text4 -> {
//blah
}
或者从one of the answers中改写演示,如下所示:-
public class RephraseDemo {
public static void main(String[] args) {
int month = 9;
int year = 2018;
int numDays = 0;
switch (month) {
case 1, 3, 5, 7, 8, 10, 12 ->{
numDays = 31;
}
case 4, 6, 9, 11 ->{
numDays = 30;
}
case 2 ->{
if (((year % 4 == 0) &&
!(year % 100 == 0))
|| (year % 400 == 0))
numDays = 29;
else
numDays = 28;
}
default ->{
System.out.println("Invalid month.");
}
}
System.out.println("Number of Days = " + numDays);
}
}
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