实体类

package demo12;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.experimental.Accessors;
import java.util.Objects;
@Data
@NoArgsConstructor
@AllArgsConstructor
@Accessors(chain = true)
public class PreStudent {private Integer id;private String name;private String age;private String address;/*** 写equals和hashCode的意义，对象name，age，只要这两个相同就认为这个两个对象相等*/@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;PreStudent that = (PreStudent) o;return name.equals(that.name) && age.equals(that.age);}@Overridepublic int hashCode() {return Objects.hash(name, age);}
}

测试

package demo12;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class TestEqualsHash {public static void main(String[] args) {PreStudent p1 = new PreStudent(1,"张三","33","河南");PreStudent p2 = new PreStudent(2,"李四","36","郑州");PreStudent p3 = new PreStudent(3,"王五","13","洛阳");PreStudent p4 = new PreStudent(4,"赵六","93","周口");List<PreStudent> preStudents = Arrays.asList(p1, p2, p3, p4);PreStudent a1 = new PreStudent(22,"张三","33","广东");// 判断a1是否存在于preStudents集合中，因为已经写了equals和hashCode方法中的，name，age所以，只要这两个属性值相等，就可以认为对象相等boolean contains = preStudents.contains(a1);System.out.println(contains);  // true// 测试2PreStudent b1 = new PreStudent(61,"小红","56","哈尔滨");PreStudent b2 = new PreStudent(62,"赵六","93","吉林");PreStudent b3 = new PreStudent(63,"王五","13","北京");List<PreStudent> nowStudents = Arrays.asList(b1, b2, b3);// 判断NowStudents存在几个与preStudents相同的List<PreStudent> equalsStudents = new ArrayList<>();for (PreStudent nowStudent : nowStudents) {if(preStudents.contains(nowStudent)) {equalsStudents.add(nowStudent);}}System.out.println(equalsStudents);// [PreStudent(id=62, name=赵六, age=93, address=吉林), PreStudent(id=63, name=王五, age=13, address=北京)]}
}