POJO类型的Java集无法添加元素
我有一个数据对象类:POJO类型的Java集无法添加元素,java,collections,set,Java,Collections,Set,我有一个数据对象类: public class MyDataObject { private String value; private String text; private Set<MyDataObject> child; // Getter & setters // Constructor public MyDataObject(final String value, final String text) { this.value
public class MyDataObject {
private String value;
private String text;
private Set<MyDataObject> child;
// Getter & setters
// Constructor
public MyDataObject(final String value, final String text) {
this.value = value;
this.text = text;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
MyDataObject that = (MyDataObject) o;
return value.equals(that.value) &&
text.equals(that.text) &&
Objects.equals(child, that.child);
}
@Override
public int hashCode() {
return Objects.hash(value, text, child);
}
}
我已经重写<代码> hash码和<代码>等于方法,以及考虑子元素。
我遗漏了什么?我对您的代码做了一些更改
childSet。添加
expect对象,但发送两个字符串。这个决心对我有用
MyDataObject myDataObject = new MyDataObject("USA", "United States");
Set<MyDataObject> childSet = new TreeSet<>(Comparator.comparing(MyDataObject::getText));
MyDataObject myDataObject1 = new MyDataObject("NY", "Bronx");
MyDataObject myDataObject2 = new MyDataObject("NY", "Manhattan");
childSet.add(myDataObject1); // This is added
childSet.add(myDataObject2); // This is not being added, returing false.
myDataObject.setChild(childSet);
myDataObject.getChild()
.stream()
.map(child -> child.getValue() + " " + child.getText())
.forEach(System.out::println);
MyDataObject MyDataObject=新的MyDataObject(“美国”、“美国”);
Set childSet=newtreeset(Comparator.comparing(MyDataObject::getText));
MyDataObject myDataObject1=新的MyDataObject(“纽约”、“布朗克斯”);
MyDataObject myDataObject2=新的MyDataObject(“纽约”、“曼哈顿”);
添加(myDataObject1);//这是增加的
childSet.add(myDataObject2);//未添加此项,返回false。
myDataObject.setChild(childSet);
myDataObject.getChild()
.stream()
.map(child->child.getValue()+“”+child.getText())
.forEach(System.out::println);
您的比较器不可用
也就是说:您为集合选择了一个比较器,当等于(对象)
方法返回false
时,该比较器返回0
,您提到的问题可以通过比较器重现。比较(MyDataObject::getValue)
。然而,比较器Comparator.comparing(MyDataObject::getText)
和Comparator.comparing(MyDataObject::getValue)
与equals不一致。请参阅javadoc,其中提到了这一点
final Comparator<MyDataObject> myDataObjectComparator = Comparator.comparing(MyDataObject::getValue);
final MyDataObject myDataObject1 = new MyDataObject("NY", "Bronx");
final MyDataObject myDataObject2 = new MyDataObject("NY", "Manhattan");
System.out.println(myDataObject1.equals(myDataObject2));
System.out.println(myDataObjectComparator.compare(myDataObject1, myDataObject2));
final Comparator myDataObjectComparator=Comparator.comparating(MyDataObject::getValue);
最终MyDataObject myDataObject1=新的MyDataObject(“纽约”、“布朗克斯”);
最终MyDataObject myDataObject2=新的MyDataObject(“纽约”、“曼哈顿”);
System.out.println(myDataObject1.equals(myDataObject2));
System.out.println(myDataObjectComparator.compare(myDataObject1,myDataObject2));
请注意,equals
表示对象不相等,而compareTo
表示0
。对于相同的两个对象。childSet.add(“NY”、“Bronx”)代码>这是无效的,应该是子集。添加(新的MyDataObject(“NY”,“Bronx”))
我无法复制您issue@Eklavya,对不起,我打错了。我是手工打字的。问题更新。我无法复制您的问题
final Comparator<MyDataObject> myDataObjectComparator = Comparator.comparing(MyDataObject::getValue);
final MyDataObject myDataObject1 = new MyDataObject("NY", "Bronx");
final MyDataObject myDataObject2 = new MyDataObject("NY", "Manhattan");
System.out.println(myDataObject1.equals(myDataObject2));
System.out.println(myDataObjectComparator.compare(myDataObject1, myDataObject2));