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获取值

Question

How to get value from Hash Map depending on key name, while we are passing custom class objects as key and value pair.In below code while i am using get method to retrieve the value by using key , i am getting compile time error. Please help me regarding this.

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);

Department.java-

package org.task;
public class Department1 {
private int deptid;
private String deptname;

public int getDeptid() {
    return deptid;
}
   public String getDeptname() {
    return deptname;
}

public Department1(int deptid, String deptname) {
    this.deptid = deptid;
    this.deptname = deptname;

}

}

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;
}
}

I want to retrieve all the details of employee by passing either department id or deptname

Answer 1

You have to override the equals method of Employee class then you can use

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

Answer 2

If you are going to use some class as key in HashMap or HashSet you need to add methods equals() and hashCode() to it. Like:

public static 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;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Employee1 employee1 = (Employee1) o;

        if (age != employee1.age) return false;
        if (id != employee1.id) return false;
        if (salary != employee1.salary) return false;
        if (!name.equals(employee1.name)) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = id;
        result = 31 * result + name.hashCode();
        result = 31 * result + age;
        result = 31 * result + (int) (salary ^ (salary >>> 32));
        return result;
    }
}

And after it will be possible to find value by new key like here:

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);
}

And if you need to execute System.out.println(value); You need to add method toString() to Department1. Like:

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

Answer 3

Check the bellow classes for getting result.

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);

}
}

//Common class for getting object value

MainData.java

/**
* @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();
}
}

Department.java

/**
* @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);
}


}

Employee.java

/**
* @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;
}


}