为什么此Java Switch-Case不起作用？

Question

So, all variables in the conditions are static strings. type itself is a string in fact.

         switch(type) {
             case (INT || TINYINT):
                 preparedStatement = setInteger(preparedStatement, value, index);  
                 break;
             case (BIGINT || LONG):
                 preparedStatement = setLong(preparedStatement, value, index);  
                 break;
             case (DATETIME || TIMESTAMP):
                 preparedStatement = setTimestamp(preparedStatement, value, index);  
                 break;
             case (MEDIUMTEXT || ENUM || TEXT || LONGTEXT || VARCHAR):
                 preparedStatement = setString(preparedStatement, value, index);  
                 break;
         }

Answer 1

First, switch statements on strings are supported in Java 7+, but not in Java 6 and before.

Next, the || operator (the logical-OR operator) only works on boolean values, not String values. But you can get the same code to be run on multiple cases by listing the cases and not breaking until past the relevant code:

switch(type) {
    case INT:
    case TINYINT:
        // This code will run for INT and TINYINT only.
        preparedStatement = setInteger(preparedStatement, value, index);  
        break;
    case BIGINT:
    case LONG:
        // This code will run for BIGINT and LONG only.
        preparedStatement = setLong(preparedStatement, value, index);  
        break;
    // etc.

Answer 2

Java 7 example :

public String getTypeOfDayWithSwitchStatement(String dayOfWeekArg) {
     String typeOfDay;
     switch (dayOfWeekArg) {
         case "Monday":
             typeOfDay = "Start of work week";
             break;
         case "Tuesday":
         case "Wednesday":
         case "Thursday":
             typeOfDay = "Midweek";
             break;
         case "Friday":
             typeOfDay = "End of work week";
             break;
         case "Saturday":
         case "Sunday":
             typeOfDay = "Weekend";
             break;
         default:
             throw new IllegalArgumentException("Invalid day of the week: " + dayOfWeekArg);
     }
     return typeOfDay;
}

Further I have never seen an OR statement inside of a switch like that. I would highly recommend not doing that.

Answer 3

假设您使用的是Java SE 7（或更高版本），并且常量是static final String ，则语法不是Java。

         case INT: case TINYINT:

Answer 4

What does this expression evaluate to?

INT || TINYINT

What are the datatypes for INT and TINYINT

I've only ever seen switch used with some primitives (and new in Java 7, string) literals or variables declared as final .

If this isn't throwing a compile error, then the || operator must be defined for whatever datatype those are. But unless that's somehow being resolved at compile time, that operator is not going to be allowed. (Again, this might be something new in Java 7 I'm not aware of.)

---

If you are trying to do " or " logic, the normative pattern (in pre-7 versions of Java at least), is:

    switch(type) {
        case INT:
        case TINYINT:
             preparedStatement = setInteger(preparedStatement, value, index);  
             break;
        case BIGINT:
        case LONG:
             preparedStatement = 
             break;

Answer 5

在Java 7及更高版本中受支持

Answer 6

You cannot use logical operators in switch statements, even with Strings. You can only test one case at a time.