我有一个抽象类，它有一个字段，其类型可以在其子类之间变化。例如：
public abstract class ABCModel {
protected String foo;
protected String bar;
protected ? baz;
}
在我的实现中，baz可能是Int或Float。例如：
public class ModelFoo {
protected Int baz;
}
public class Modelbar {
protected Float baz;
}
首先，让我问一下这是否是Java中有效/可接受的设计模式？我选择了这种模式，因为我想抽象出共享方法中大部分繁琐的样板。
根据我的实现方式，我得到了这个错误的变体：
incompatible types: CAP#1 cannot be converted to BidAsk
where CAP#1 is a fresh type-variable:
CAP#1 extends Object from capture of ?
这让我相信我做错了什么。
我发布的示例与我的实际代码相比有点微不足道，其中这个泛型隐藏在嵌套的哈希表中。我试图在投入过多之前决定我在做什么是Java中的智能设计。
我已经尝试过搜索，但可能没有正确地阐述术语。
感谢。
答案 0 :(得分：3)
您要问的是泛型的基本用法：
public abstract class ABCModel<T> {
private T baz;
public T getBaz() { return baz; }
public void setBaz(T baz) { this.baz = baz; }
}
public class IntModel extends ABCModel<Integer> { // baz is of type Integer
}
public class FloatModel extends ABCModel<Float> { // baz is of type Float
}
IntModel m1 = new IntModel();
Integer i = m1.getBaz();
FloatModel m2 = new FloatModel();
Float f = m2.getBaz();
答案 1 :(得分：1)
无法在Java中覆盖字段。但是，您可以使用泛型方法。
/*****************Nested Accordion************************/
input:focus { outline: none; }
a {
color: #000000;
outline: none !important;
}
ul{
margin-top:20px;
list-style-type: none;
margin: 0;
padding: 0;
}
.singleColumn li h2{padding-left:20px;}
.docsAccordion {
background-color: #fbf5db;
font-family: 'Helvetica';
font-weight: bold;
font-size: 1em;
color: #000000;
}
ul.docsAccordion > li{
border-bottom: thick solid #ffffff;
text-align:left;
}
/***turn off links inside the accordion h3 h2 and links***/
ul.docsAccordion > li a:link{
text-decoration:none !important;
color:#000000 !important;
}
ul.docsAccordion > li a:hover{
text-decoration:none;
color:#000000;
padding:0px;
margin:0px;
}
ul.docsAccordion > li a:visited{
text-decoration:none !important;
color:#000000 !important;
}
ul.docsAccordion > li h2 a:hover{
text-decoration:none !important;
color:#000000 !important;
}
ul.docsAccordion > li h2 a:visited{
text-decoration:none !important;
color:#000000 !important;
}
.dataTable a { /***turn on links inside the datatable***/
text-decoration:underline !important;
}
li.nestedElems{ /*list inside accordion*/
padding-left:5px !important;
margin-left:0px !important;
border-bottom: none;
background-color:#ffffff;
text-align:left;
border: 1px solid #eee6b5;
}
ul.insideAccor > li{
padding: 10px 0 10px 0;
background-color: #ffffff;
margin-bottom: 2px;
margin-left: 0px;
text-align: left;
font-weight: normal;
font-size: 1.2em;
}
table#docListTable > tbody > tr > td a:visited{
text-decoration:none !important;
color:#800080;
}
ul.insideAccorList > li{
padding: 5px 0 5px 60px;
background-color: #ffffff;
margin-bottom: 2px;
text-align: left;
font-weight: normal;
font-size: 1.2em;
border-top:1px solid #eee6b5;
}
/*style links inside accordion list*/
ul.insideAccorList li a:link{
color:#0000ff !important;
text-decoration:underline !important;
}
ul.insideAccorList li a:hover{
color:#0000ff !important;
text-decoration:underline !important;
}
ul.insideAccorList li a:visited{
text-decoration:underline !important;
color:#800080 !important;
}
ul.indentList > li{
padding-left:20px;
}
.noPadTop{
padding-top: 0 !important;
}
li.nestedElemAccor{
margin-top: -20px;
}
h2.ui-accordion-header.ui-state-default { /*add arrowhead*/
font-size:1.2em;
background-image: url("/site-resources/resource-files/img/arrow-lg.png");
background-repeat: no-repeat;
background-position:0% 50%;
width:100%;
}
h2.ui-accordion-header.ui-state-active { /*add arrowhead*/
font-size:1.2em;
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background-repeat: no-repeat;
background-position:0% 50%;
width:100%;
}
h3.ui-accordion-header.ui-state-default { /*add arrowhead*/
font-size:1.2em;
padding-left:15px;
background-image: url("/site-resources/resource-files/img/arrow-sm.png");
background-repeat: no-repeat;
background-position:5px 3px;
width:95%;
}
h3.ui-accordion-header.ui-state-active { /*add arrowhead*/
font-size:1.2em;
padding-left:15px;
background-image: url("/site-resources/resource-files/img/arrow-sm-dn.png");
background-repeat: no-repeat;
background-position:5px 3px;
width:95%;
}
li.NestElemTitle{
background-color: #ffffff;
padding: 3px 0px 3px 0px;
text-align:left;
}
.singleColumn h2{
font-size:1.2em;
margin-left:5px;
}
.singleColumn h3{
font-size:1.2em;
margin-left:10px;
}然后
<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.11.0/jquery-ui.min.js"></script>
<script src="//cdn.datatables.net/1.10.11/js/jquery.dataTables.min.js"></script>
<link href="//cdn.datatables.net/1.10.11/css/jquery.dataTables.min.css" rel="stylesheet"/>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<ul class = "docsAccordion">
<li>
<h2><a href="#">(February 19, 2013 - May 12)</a></h2>
</li>
<li>
<h2><a href="#">(February 19, 2012 - May 11)</a></h2>
</li>
<!-- element which hold Individual class in accordian -->
<li>
<h2><a href="#">September 10, 2007</a></h2>
<li>
<h2><a href="#">(February 19, 2011 - May 10)</a></h2>
<ul class="docsAccordion nestedElemAccor">
<li class = "nestedElems">
<h3><a href="#">December 2001 (4 Meeting days)</a></h3>
<ul class="insideAccor">
<li>
<p>gsdrfg</p>
</li>
</ul>
</li>
<li class = "nestedElems">
<h3><a href="#">February 2002 (7 Meeting days)</a></h3>
</li>
<li class="nestedElems">
<h3><a href="#">November 2001 (6 meetings days)</a></h3>
<ul class="insideAccor">
<li>
<ul class="insideAccorList">
<li><a href="http://www.google.ca">Monday February 3</a></li>
<li><a href="http://www.bing.ca">Tuesday February 4</a></li>
<li><a href="http://www.yahoo.ca">Wednesday Februaary 5</a></li>
<li><a href="http://www.apple.ca">Thursday February 6</a></li>
<li><a href="http://www.sony.ca">Tuesday February 11</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
<!-- END element which hold Individual class in accordian -->
<li>
<h2><a href="#">(February 19, 2010 - May 09)</a></h2>
</li>
<li>
<h2><a href="#"> (February 19, 2009 - May 08)</a></h2>
</li>
</ul>答案 2 :(得分：1)
这是一种可接受的模式，但您应该更加具体地了解您的泛型：
public abstract class ABCModel<T extends Number> {
protected String foo;
protected String bar;
protected T baz;
public T getBaz() {
return baz;
}
}
之后你可以扩展你的模型：
public class ModelFoo extends ABCModel<Integer> {
// No need to specify again baz.
}