Question

我正在

incompatible types; inferred type argument(s) java.lang.Object do not conform to bounds of type variable(s) T
[ERROR] found   : <T>int
[ERROR] required: int
[ERROR] -> [Help 1]

我的方法

private <T extends Comparable<T>> int useComparator(final Object o1, final Object o2, final String property) {
    final T s1 = new PropertyModel<T>(o1, property).getObject();
    final T s2 = new PropertyModel<T>(o2, property).getObject();
    return s1.compareTo(s2);
}

其中PropertyModel是org.apache.wicket.model.PropertyModel，但实际上这并不重要（这个类只返回某个字段的值，顺便说一句：例如，在Spring中是否存在一些具有类似功能的类？）。

问题在于调用该方法：

return this.useComparator(o1, o2, sortProperty);

我可以通过

解决这个问题

return this.<Comparable> useComparator(o1, o2, sortProperty);

但我想知道..在Eclipse和NetBeans中编译这样的代码时我没有问题。据我所知，我正在使用相同的java，但在Maven中，我从帖子的开头得到了错误。我错过了一些编译器标志吗？

不确定这是否有帮助，但我的Maven版本是：

> mvn -version
Apache Maven 3.0.4 (r1232337; 2012-01-17 09:44:56+0100)
Maven home: c:\Programs\apache-maven-3.0.4
Java version: 1.6.0_37, vendor: Sun Microsystems Inc.
Java home: c:\Java\jdk1.6.0_37\jre
Default locale: sk_SK, platform encoding: Cp1250
OS name: "windows 7", version: "6.1", arch: "amd64", family: "windows"

来自pom.xml的Maven编译器插件设置：

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <version>2.5.1</version>
    <inherited>true</inherited>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
        <source>1.6</source>
        <target>1.6</target>
        <encoding>UTF-8</encoding>
    </configuration>
</plugin>

编辑：已添加请求的代码

创建wicket项目（仅用于依赖项）。我使用Wicket Quickstart page来生成maven项目。我用过：

mvn archetype：generate -DarchetypeGroupId = org.apache.wicket -DarchetypeArtifactId = wicket-archetype-quickstart -DarchetypeVersion = 6.6.0 -DgroupId = net.betlista -DartifactId = stackoverflow -DarchetypeRepository = https://repository.apache.org/ -DinteractiveMode =假

将项目导入您喜欢的IDE。

使用此JUnit测试来模拟问题：

package net.betlista;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import junit.framework.Assert;

import org.apache.wicket.extensions.markup.html.repeater.util.SortParam;
import org.apache.wicket.model.PropertyModel;
import org.junit.Test;

public class ComparatorTest {

    @Test
    public void test() {
        final ArrayList<Person> persons = new ArrayList<Person>();

        final Person alice = new Person("Alice", 30);
        persons.add(alice);
        final Person bob = new Person("Bob", 20);
        persons.add(bob);

        Collections.sort(persons, new PropertyComparator(new SortParam<String>("name", true)));
        Assert.assertEquals(alice, persons.get(0));
        Assert.assertEquals(bob, persons.get(1));

        Collections.sort(persons, new PropertyComparator(new SortParam<String>("name", false)));
        Assert.assertEquals(alice, persons.get(1));
        Assert.assertEquals(bob, persons.get(0));

        Collections.sort(persons, new PropertyComparator(new SortParam<String>("age", true)));
        Assert.assertEquals(alice, persons.get(1));
        Assert.assertEquals(bob, persons.get(0));

        Collections.sort(persons, new PropertyComparator(new SortParam<String>("age", false)));
        Assert.assertEquals(alice, persons.get(0));
        Assert.assertEquals(bob, persons.get(1));
    }

    static class Person {
        String name;
        Integer age;

        public Person(final String name, final Integer age) {
            this.name = name;
            this.age = age;
        }
    }

    private static class PropertyComparator implements Comparator<Object> {

        private SortParam<String> sort;

        public PropertyComparator(final SortParam<String> sort) {
            this.sort = sort;
        }

        @Override
        public int compare(final Object o1, final Object o2) {
            final int dir = sort.isAscending() ? 1 : -1;

            final String sortProperty = sort.getProperty();
            return dir * this.useComparator(o1, o2, sortProperty);
        }

        private <T extends Comparable<T>> int useComparator(final Object o1, final Object o2, final String property) {
            final T p1 = new PropertyModel<T>(o1, property).getObject();
            final T p2 = new PropertyModel<T>(o2, property).getObject();
            return p1.compareTo(p2);
        }

    }

}

在我的环境中，这在Eclipse中运行良好，但在尝试使用

编译时失败

mvn clean install

当我尝试将useComparator移出PropertyComparator并使其静止无效时......

不兼容的类型（泛型）

0 个答案: