Apex中文手册

if语句后面可以跟一个可选的else if ... else语句，这对于使用single if ... else if语句测试各种条件非常有用。

语法：

if boolean_expression_1 {
   /* Executes when the boolean expression 1 is true */
} else if boolean_expression_2 {
   /* Executes when the boolean expression 2 is true */
} else if boolean_expression_3 {
   /* Executes when the boolean expression 3 is true */
} else {
   /* Executes when the none of the above condition is true */
}

例如：

假设，我们的化工公司有两类客户：高级和正常。 根据客户类型，我们应该提供折扣和其他好处，如售后服务和支持。 下面是这个的实现。

//Execute this code in Developer Console and see the Output
String customerName = 'Glenmarkone'; //premium customer
Decimal discountRate = 0;
Boolean premiumSupport = false;
if (customerName == 'Glenmarkone') {
    discountRate = 0.1; //when condition is met this block will be executed
    premiumSupport = true;
    System.debug('Special Discount given as Customer is Premium');
}
else if (customerName == 'Joe') {
    discountRate = 0.5; //when condition is met this block will be executed
    premiumSupport = false;
    System.debug('Special Discount not given as Customer is not Premium');
}
else {
    discountRate = 0.05; //when condition is not met and customer is normal
    premiumSupport = false;
    System.debug('Special Discount not given as Customer is not Premium');
}