ImmutableClass.java
import java.util.Date;
/**
* Always remember that your instance variables will be either mutable or immutable.
* Identify them and return new objects with copied content for all mutable objects.
* Immutable variables can be returned safely without extra effort.
* */
public final class ImmutableClass
{ /** * Integer class is immutable as it does not provide any setter to change its content * */ private final Integer immutableField1; /** * String class is immutable as it also does not provide setter to change its content * */ private final String immutableField2; /** * Date class is mutable as it provide setters to change various date/time parts * */ private final Date mutableField; //Default private constructor will ensure no unplanned construction of class private ImmutableClass(Integer fld1, String fld2, Date date) { this.immutableField1 = fld1; this.immutableField2 = fld2; this.mutableField = new Date(date.getTime()); } //Factory method to store object creation logic in single place public static ImmutableClass createNewInstance(Integer fld1, String fld2, Date date) { return new ImmutableClass(fld1, fld2, date); } //Provide no setter methods /** * Integer class is immutable so we can return the instance variable as it is * */ public Integer getImmutableField1() { return immutableField1; } /** * String class is also immutable so we can return the instance variable as it is * */ public String getImmutableField2() { return immutableField2; } /** * Date class is mutable so we need a little care here. * We should not return the reference of original instance variable. * Instead a new Date object, with content copied to it, should be returned. * */ public Date getMutableField() { return new Date(mutableField.getTime()); } @Override public String toString() { return immutableField1 +" - "+ immutableField2 +" - "+ mutableField; }
}