Question

我有以下代码：

$sql = "Select * from table_name where catregory = ".$_POST'category'];
// execute the query.

$sub = "<select name='sub-category'>";
foreach(result from database as $row) {
     $sub .= "<option value='$row->id'>$row->name</option>";
}

$sub .= "</select>";

echo $sub;

其中UniqueConstraintViolation是接口扩展的javax.validation.ConstraintViolation 和UniqueConstraintViolationImpl是类实现的UniqueConstraintViolation

编译时我得到以下错误

java：42：错误：找不到合适的方法添加（UniqueConstraintViolation） violations.add（冲突）; ^ 方法Collection.add（CAP＃1）不适用（参数不匹配; UniqueConstraintViolation无法转换为CAP＃1）方法Set.add（CAP＃1）不适用（参数不匹配; UniqueConstraintViolation无法转换为CAP＃1），其中CAP＃1是一个新的类型变量： CAP＃1扩展了ConstraintViolation的捕获？扩展ConstraintViolation C：\ workspace \ zcts-travel \ crud-rest \ src \ main \ java \ ru \ zcts \ crud \ AbstractResource.java:43：错误：不兼容类型：设置无法转换为设置＆gt; 抛出新的javax.validation.ConstraintViolationException（违规）;
UniqueConstraintViolation violation = new UniqueConstraintViolationImpl();
Set<? extends javax.validation.ConstraintViolation> violations = new HashSet<UniqueConstraintViolation>();
violations.add(violation);
throw new javax.validation.ConstraintViolationException(violations);

我只想传递javax.validation.ConstraintViolationException构造函数，使用我自己的javax.validation.ConstraintViolation实现。我怎么能这样做？

Answer 1

Set<? extends javax.validation.ConstraintViolation> violations = new HashSet<UniqueConstraintViolation>();
violations.add(violation);

您无法将null以外的任何内容添加到voilations，因为它使用? extends javax.validation.ConstraintViolation。

请在此处阅读：Java Generic with ArrayList <? extends A> add element

Answer 2

所以有你的约束：

interface UniqueConstraintViolation extends ConstraintViolation<YourClass> {

}

public class UniqueConstraintViolationImpl implements UniqueConstraintViolation {
    /* your impl here */
}

这将编译：

UniqueConstraintViolation violation = new UniqueConstraintViolationImpl();

Set<UniqueConstraintViolation> violations = new HashSet<UniqueConstraintViolation>();
violations.add(violation);
throw new ConstraintViolationException(violations);

Set中的GenericsAdd（捕获<！ - ？extends ConstraintViolation - >）无法应用于（ConstraintViolation）

2 个答案: