Java 当我们将自定义类对象作为键和值传递时，如何根据键名从HashMap中获取值

当我们将自定义类对象作为键和值对传递时，如何根据键名从哈希映射中获取值。在下面的代码中，当我使用get方法通过键检索值时，我遇到编译时错误。请帮我解决这个问题

HashMap<Employee1, Department1> hm= new HashMap<Employee1, Department1>();
    hm.put(new Employee1(0, "name1", 25, 46666), new Department1(0, "developer"));
    hm.put(new Employee1(0, "name2", 50, 40000), new Department1(0, "tester"));
    hm.put(new Employee1(0, "name3", 34, 3000), new Department1(0, "hr"));
    hm.put(new Employee1(0, "name4",30, 26666), new Department1(0, "manager"));
    hm.put(new Employee1(0, "name5",28, 15000), new Department1(0, "accountant"));

    Department1 value = (Department1) hm.get(0, "name5",28, 15000);
    System.out.println(value);

Employee.java-

package org.task;
public class Employee1 {
private int id;
private String name;
private int age;
private long salary;

public int getId() {
    return id;
}

public String getName() {
    return name;
}

public int getAge() {
    return age;
}

public long getSalary() {
    return salary;
}

public Employee1(int id, String name, int age, int salary) {
    this.id = id;
    this.name = name;
    this.age = age;
    this.salary = salary;
}
}

---

我想通过传递部门id或部门名称来检索员工的所有详细信息

您必须重写employee类的equals方法 然后你可以用

Employee1 testEmp =  new Employee1(0, "name5",28, 15000);
Department1 value = (Department1) hm.get(testEmp);
System.out.println(value);

---

如果要使用某个类作为HashMap或HashSet中的键，则需要向其中添加方法equals（）和hashCode（）。 比如：

之后，可以通过如下所示的新键查找值：

public static void main(String[] args) throws Exception {
    HashMap<Employee1, Department1> hm = new HashMap<Employee1, Department1>();
    hm.put(new Employee1(0, "name1", 25, 46666), new Department1(0, "developer"));
    hm.put(new Employee1(0, "name2", 50, 40000), new Department1(0, "tester"));
    hm.put(new Employee1(0, "name3", 34, 3000), new Department1(0, "hr"));
    hm.put(new Employee1(0, "name4", 30, 26666), new Department1(0, "manager"));
    hm.put(new Employee1(0, "name5", 28, 15000), new Department1(0, "accountant"));

    Department1 value = hm.get(new Employee1(0, "name5", 28, 15000));
    System.out.println(value);
}

---

检查下面的类以获得结果

MainTest.java

import java.util.HashMap;

/**
* @author Rajesh
*
*/
public class MainTest {

public static void main(String []args)
{
    HashMap<Employee, Department> hm= new HashMap<Employee, Department>();
    hm.put(new Employee(0, "name0", 20, 46666), new Department(0, "developer"));
    hm.put(new Employee(0, "name0", 25, 46666), new Department(0, "tester"));
    hm.put(new Employee(0, "name3", 34, 3000), new Department(0, "hr"));
    hm.put(new Employee(0, "name4",40, 26666), new Department(0, "manager"));
    hm.put(new Employee(0, "name5",28, 15000), new Department(0, "accountant"));
    Department value = (Department) hm.get(new Employee(0, "name3", 34, 3000));
    System.out.println(value);

}
}

---

你的问题不太清楚。你所说的“密钥名”是什么意思。如果这是

Employee1

的一个属性，那么也可以将该类添加到您的帖子中。什么是“cte”？重写了equal和hashode（）并遵循上面的代码，但仍然没有得到所需的输出。输出为-org.task。Department1@87816dtrySystem.out.println（value.getDeptid（））；它的打印java对象是DeparteMet。覆盖部门的字符串方法以正确打印值如果我的答案对您有帮助，您可以投票并接受。祝你好运

public static void main(String[] args) throws Exception {
    HashMap<Employee1, Department1> hm = new HashMap<Employee1, Department1>();
    hm.put(new Employee1(0, "name1", 25, 46666), new Department1(0, "developer"));
    hm.put(new Employee1(0, "name2", 50, 40000), new Department1(0, "tester"));
    hm.put(new Employee1(0, "name3", 34, 3000), new Department1(0, "hr"));
    hm.put(new Employee1(0, "name4", 30, 26666), new Department1(0, "manager"));
    hm.put(new Employee1(0, "name5", 28, 15000), new Department1(0, "accountant"));

    Department1 value = hm.get(new Employee1(0, "name5", 28, 15000));
    System.out.println(value);
}

    @Override
    public String toString() {
        return "Department1{" +
                "deptid=" + deptid +
                ", deptname='" + deptname + '\'' +
                '}';
    }

import java.util.HashMap;

/**
* @author Rajesh
*
*/
public class MainTest {

public static void main(String []args)
{
    HashMap<Employee, Department> hm= new HashMap<Employee, Department>();
    hm.put(new Employee(0, "name0", 20, 46666), new Department(0, "developer"));
    hm.put(new Employee(0, "name0", 25, 46666), new Department(0, "tester"));
    hm.put(new Employee(0, "name3", 34, 3000), new Department(0, "hr"));
    hm.put(new Employee(0, "name4",40, 26666), new Department(0, "manager"));
    hm.put(new Employee(0, "name5",28, 15000), new Department(0, "accountant"));
    Department value = (Department) hm.get(new Employee(0, "name3", 34, 3000));
    System.out.println(value);

}
}

/**
* @author Rajesh
*
*/

import java.lang.reflect.Field;

public class MainData<E> {

Class c;
public String toStringData(E e1) {
    // TODO Auto-generated method stub
    StringBuffer getData= new StringBuffer();
    try {
        c=e1.getClass();;
         Field fields[] = c.getDeclaredFields();
         for (Field field : fields) {
             Object fieldValue = field.get(e1);
             getData.append(field.getName()+":"+fieldValue+",");
        }
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return getData.toString();
}
}

/**
* @author Rajesh
*
*/

public class Department extends MainData<Department> {

public int deptid;
public String deptname;
public int getDeptid() {
    return deptid;
}
public void setDeptid(int deptid) {
    this.deptid = deptid;
}
public String getDeptname() {
    return deptname;
}
public void setDeptname(String deptname) {
    this.deptname = deptname;
}
public Department(int deptid, String deptname) {
    this.deptid = deptid;
    this.deptname = deptname;
}

@Override
public String toString() {
    // TODO Auto-generated method stub
    //for getting object value
    return super.toStringData(this);
}


}

/**
* @author Rajesh
*
*/

public class Employee {

private int id;
private String name;
private int age;
private long salary;
public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public int getAge() {
    return age;
}
public void setAge(int age) {
    this.age = age;
}
public long getSalary() {
    return salary;
}
public void setSalary(long salary) {
    this.salary = salary;
}
public Employee(int id, String name, int age, long salary) {
    this.id = id;
    this.name = name;
    this.age = age;
    this.salary = salary;
}

@Override
public boolean equals(Object obj) {
    Employee employee = (Employee) obj;
    //compare all the property 
    if (this.age != employee.age) return false;
    if (this.id != employee.id) return false;
    if (this.salary != employee.salary) return false;
    if (!this.name.equals(employee.name)) return false;
    return true;
}

@Override
public int hashCode() {
    //return any unique code
    return this.id+this.name.hashCode()+this.age+(int)this.salary;
}


}