如何使用java.util.Objects实现equals()和hashCode()方法？
本示例将向您展示如何使用类实现equals()andhashCode()对象java.util.Objects。的Objects类别提供一组实用的方法来工作，对象，如比较是否相等两个对象和计算的哈希码。其他方法包括对象null检查方法，对象到字符串方法等。
为了演示equals()和hash()方法，我们将创建一个简单的POJOStudent，它具有id，name和等几个属性dateOfBirth。
package org.nhooo.example.util;
import java.time.LocalDate;
import java.util.Objects;
public class Student {
private Long id;
private String name;
private LocalDate dateOfBirth;
public Student() {
}
public Student(Long id, String name, LocalDate dateOfBirth) {
this.id = id;
this.name = name;
this.dateOfBirth = dateOfBirth;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public LocalDate getDateOfBirth() {
return dateOfBirth;
}
public void setDateOfBirth(LocalDate dateOfBirth) {
this.dateOfBirth = dateOfBirth;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Student that = (Student) o;
return Objects.equals(this.id, that.id)
&& Objects.equals(this.name, that.name)
&& Objects.equals(this.dateOfBirth, that.dateOfBirth);
}
@Override
public int hashCode() {
return Objects.hash(id, name, dateOfBirth);
}
}在类中使用Objects.equals()和Objects.hash()方法Student可使equals()方法和hashCode()方法的实现简洁，易于阅读和理解。该Objects实用类将在这意味着它会检查对象的空场空安全的方式进行操作。
下面的代码片段将演示Student类的用法。它将使用该equals()方法比较对象并打印出对象的计算出的哈希码。
package org.nhooo.example.util;
import java.time.LocalDate;
import java.time.Month;
public class EqualsHashCodeExample {
public static void main(String[] args) {
Student student1 = new Student(1L, "Alice", LocalDate.of(1990, Month.APRIL, 1));
Student student2 = new Student(1L, "Alice", LocalDate.of(1990, Month.APRIL, 1));
Student student3 = new Student(2L, "Bob", LocalDate.of(1992, Month.DECEMBER, 21));
System.out.println("student1.equals(student2) = " + student1.equals(student2));
System.out.println("student1.equals(student3) = " + student1.equals(student3));
System.out.println("student1.hashCode() = " + student1.hashCode());
System.out.println("student2.hashCode() = " + student2.hashCode());
System.out.println("student3.hashCode() = " + student3.hashCode());
}
}这是上面代码片段的结果：
student1.equals(student2) = true student1.equals(student3) = false student1.hashCode() = 1967967937 student2.hashCode() = 1967967937 student3.hashCode() = 6188033
实现equals()andhashCode()方法的另一种方法是使用ApacheCommonsLang库。它的示例可以在这里看到：如何使用ApacheCommons实现hashCode和equals方法？