首先我们创建一个类
public class People {
private String name;
private String address;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public People() {
super();
}
public People(String name, String address) {
super();
this.name = name;
this.address = address;
}
@Override
public String toString() {
return "People [name=" + name + ", address=" + address + "]";
}
}
该类没有重写hashcode和equals方法
下面我们进行比较
public static void main(String[] args) {
People p1 = new People("a", "A");
People p2 = new People("a", "A");
People p3 = new People("b", "B");
System.err.println(p1);
System.err.println(p2);
System.err.println(p3);
System.err.println(p1.equals(p2));
System.err.println(p1 == p2);
System.err.println(p1.equals(p3));
System.err.println(p1 == p3);
}
结果为：
说明如果没有重写equals()方法，则equals和==比较的都是地址。每生成一个对象，虚拟机都会重新生成一个地址，因此比较结果都为false
我们加上hashcode和equals方法
public class People {
private String name;
private String address;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public People() {
super();
}
public People(String name, String address) {
super();
this.name = name;
this.address = address;
}
@Override
public String toString() {
return "People [name=" + name + ", address=" + address + "]";
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((address == null) ? 0 : address.hashCode());
result = prime * result + ((name == null) ? 0 : name.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;
People other = (People) obj;
if (address == null) {
if (other.address != null)
return false;
} else if (!address.equals(other.address))
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
}
再次运行实例，结果为：
说明如果重写equals()方法，则==比较的是地址，equals比较的是对象中的内容