A Person Class Constructor public Person String the
A Person Class Constructor public Person( String the. Name, Date birth. Date, Date death. Date ) { // check that birth. Date <= death. Date // consistent( ) is a private helper method if ( the. Name != null && consistent(birth. Date, death. Date)) { name = the. Name; born = new Date( birth. Date ); // copy the birthe. Date object if( death. Date == null ) died = null; else died = new Date( death. Date ); } else { // later we’ll deal with errors differently System. out. println( "Inconsistent Person parameters. “ ); System. exit( 0 ); } } 9
Designing a Person Class: The Class Invariant /** Class invariant: A Person always has a date of birth, and if the Person has a date of death, then the date of death is equal to or later than the date of birth. To be consistent, name and birth. Date must not be null. If there is no date of death (death. Date == null), that is consistent with any birth. Date. Otherwise, the birth. Date must come before or be equal to the death. Date. precedes() is a boolean method in Date */ private boolean consistent(Date birth. Date, Date death. Date) { if( birth. Date == null ) return false; if( death. Date == null ) return true; return birth. Date. precedes( death. Date ) || birth. Date. equals( death. Date ); } 10
equals ﻣﺘﺪ : Person ﻃﺮﺍﺣی کﻼﺱ public boolean equals(Person other. Person) { This is the equals method for the if (other. Person == null) String class return false; else return name. equals(other. Person. name) && born. equals(other. Person. born) && dates. Match(died, other. Person. died); } This is the equals method for the Date class 14 This is a special helper method that handles null Date references
Dates. Match ﻣﺘﺪ کﻤکی : Person ﻃﺮﺍﺣی کﻼﺱ /** To match date 1 and date 2 must either be the same date or both be null. */ private boolean dates. Match( Date date 1, Date date 2 { if( date 1 == null ) return date 2 == null; // else if( date 2 == null ) // return false; // else // both dates are not null return date 1. equals( date 2 ); } 15 ) both null is ok && date 1 != null only one null not ok
Date ﺳﺎﺯﻧﺪﻩ ی کپی ﺑﺮﺍی کﻼﺱ // a class that does not use composition can // simply copy the values of the primitive instance // variables public Date( Date a. Date ) { if( a. Date == null ) // Not a real date object parameter { // we’ll handle errors differently later System. out. println( "Fatal Error. “ ); System. exit( 0 ); } // just copy the primitive variables using assignment // month is a String which is NOT primitive, but that’s ok month = a. Date. month; day = a. Date. day; year = a. Date. year; 18 }
Person ﺳﺎﺯﻧﺪﻩ ی کپی ﺑﺮﺍی کﻼﺱ public Person( Person original ) { if( original == null ) { System. out. println( "Fatal error. “ ); System. exit( 0 ); } name = original. name; born = new Date( original. born ); if( original. died == null ) died = null; else died = new Date( original. died ); } 21
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