java 如何存储唯一对象以避免java Set中的重复？
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How to Store unique objects to avoid the duplicates in java Set?
提问by iamjustcoder
How to Store unique objects to avoid the duplicates in java Set?
如何存储唯一对象以避免java Set中的重复？
For example
例如
Consider Employee object which (Employee Id, name, salary....)
考虑 Employee 对象（员工 ID、姓名、薪水....）
list of employee of objects need to add in the Set. We need to restrict the Set for the duplicate elements which need to identify by the "Employee Id.
对象的雇员列表需要添加到集合中。我们需要限制需要通过“员工 ID.
What are the best way's to do?
最好的方法是什么？
回答by Dirk
If you are using an implementation of a java.util.Set, it should not allow duplicates as long as your equalsand hashCodemethods are implemented properly. Not sure why you have hashmap and hashtable as tags on your question though. Maybe you should rephrase your question and add the code that gives you issues?
如果您正在使用 a 的实现java.util.Set，则只要您的equals和hashCode方法正确实现，就不应该允许重复。不知道为什么你有 hashmap 和 hashtable 作为你的问题的标签。也许您应该重新表述您的问题并添加给您带来问题的代码？
Edit: considering your edit:
编辑：考虑您的编辑：
If you use a Set, your Employee should have the following methods:
如果您使用 a Set，您的 Employee 应该有以下方法：
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((id == null) ? 0 : id.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Employee other = (Employee) obj;
if (id == null) {
if (other.id != null)
return false;
} else if (!id.equals(other.id))
return false;
return true;
}
回答by hipokito
Similarly to @Dirk, you can also use HashCodeBuilder and EqualsBuilder from org.apache.commons.
与@Dirk 类似，您也可以使用 org.apache.commons 中的 HashCodeBuilder 和 EqualsBuilder。
It would look like this:
它看起来像这样：
@Override
public int hashCode() {
return new HashCodeBuilder()
.append(id)
.append(name)
.append(salary)
.toHashCode();
}
@Override
public boolean equals(Object obj) {
if (obj instanceof Employee) {
final Employee employee = (Employee) obj;
return new EqualsBuilder()
.append(id, employee.id)
.append(id, employee.name)
.append(id, employee.salary)
.isEquals();
} else {
return false;
}
}
回答by saum22
Set Stores unique object only
Set 仅存储唯一对象
Eg:
例如：
Set set = new HashSet();
// Add elements to the set
set.add("a");//true
set.add("b");//true
set.add("c");//true
set.add("d");//true
set.add("a");//false
add will return false when you will try to store the object which is already in the Set
当您尝试存储已经在 Set 中的对象时，add 将返回 false
