How to implement hashCode and equals method

Question

How should I implement hashCode() and equals() for the following class in Java?

class Emp  {   int empid ; // unique across all the departments    String name;   String dept_name ;   String code ; // unique for the department  } 

Answer 1

in Eclipse right mouse click-> source -> generate hashCode() and equals() gives this:

/* (non-Javadoc)  * @see java.lang.Object#hashCode()  */ @Override public int hashCode() {     final int prime = 31;     int result = 1;     result = prime * result + (code == null ? 0 : code.hashCode());     return result; } /* (non-Javadoc)  * @see java.lang.Object#equals(java.lang.Object)  */ @Override public boolean equals(Object obj) {     if (this == obj)         return true;     if (obj == null)         return false;     if (!(obj instanceof Emp))         return false;     Emp other = (Emp) obj;     return code == null ? other.code == null : code.equals(other.code); } 

I've selected code as a unique field

Answer 2

try this code, use org.apache.commons.lang3.builder

public int hashCode() {     return new HashCodeBuilder(17, 31). // two randomly chosen prime numbers         append(empid).         append(name).         append(dept_name ).         append(code ).         toHashCode(); }  public boolean equals(Object obj) {      if (obj == this)         return true;     if (!(obj instanceof Person))         return false;      Emp rhs = (Emp) obj;     return new EqualsBuilder().         // if deriving: appendSuper(super.equals(obj)).         append(name, rhs.name).         isEquals(); }