java對象對比之comparable和comparator的區別

public static void main(String[] args){
        int a = 10;
        int b = 20;
        System.out.println(a>b);
        System.out.println(a==b);
        System.out.println(a<b);

        char c1 = 'A';
        char c2 = 'B';
        System.out.println(c1>c2);
        System.out.println(c1==c2);
        System.out.println(c1<c2);

        boolean b1 = true;
        boolean b2 =false;
        System.out.println(b1==b2);
        System.out.println(b1!=b2);
    }

public class Main{
    public static void main(String[] args){
       Card c1 = new Card(1,"♠");
        Card c2 = new Card(2,"♠");
        Card c3 = c1;
        System.out.println(c1==c2);
        System.out.println(c1==c3);
//        System.out.println(c1>c2);  編譯報錯
//        System.out.println(c1<c2);  編譯報錯
    }

}
class  Card{
    public int rank;
    public String suit;
     public Card(int rank,String suit){
         this.rank = rank;
         this.suit = suit;
     }
}

public interface Comparable<T> {
    /**
     * Compares this object with the specified object for order.  Returns a
     * negative integer, zero, or a positive integer as this object is less
     * than, equal to, or greater than the specified object.
     *
     * <p>The implementor must ensure <tt>sgn(x.compareTo(y)) ==
     * -sgn(y.compareTo(x))</tt> for all <tt>x</tt> and <tt>y</tt>.  (This
     * implies that <tt>x.compareTo(y)</tt> must throw an exception iff
     * <tt>y.compareTo(x)</tt> throws an exception.)
     *
     * <p>The implementor must also ensure that the relation is transitive:
     * <tt>(x.compareTo(y)&gt;0 &amp;&amp; y.compareTo(z)&gt;0)</tt> implies
     * <tt>x.compareTo(z)&gt;0</tt>.
     *
     * <p>Finally, the implementor must ensure that <tt>x.compareTo(y)==0</tt>
     * implies that <tt>sgn(x.compareTo(z)) == sgn(y.compareTo(z))</tt>, for
     * all <tt>z</tt>.
     *
     * <p>It is strongly recommended, but <i>not</i> strictly required that
     * <tt>(x.compareTo(y)==0) == (x.equals(y))</tt>.  Generally speaking, any
     * class that implements the <tt>Comparable</tt> interface and violates
     * this condition should clearly indicate this fact.  The recommended
     * language is "Note: this class has a natural ordering that is
     * inconsistent with equals."
     *
     * <p>In the foregoing description, the notation
     * <tt>sgn(</tt><i>expression</i><tt>)</tt> designates the mathematical
     * <i>signum</i> function, which is defined to return one of <tt>-1</tt>,
     * <tt>0</tt>, or <tt>1</tt> according to whether the value of
     * <i>expression</i> is negative, zero or positive.
     *
     * @param   o the object to be compared.
     * @return  a negative integer, zero, or a positive integer as this object
     *          is less than, equal to, or greater than the specified object.
     *
     * @throws NullPointerException if the specified object is null
     * @throws ClassCastException if the specified object's type prevents it
     *         from being compared to this object.
     */
    public int compareTo(T o);
}

public class Main{
    public static void main(String[] args){
        Card c1 = new Card(1,"♠");
        Card c2 = new Card(2,"♠");
        Card c3 = c1;
        System.out.println(c1.compareTo(c2));
        System.out.println(c1.compareTo(c3));
        System.out.println(c2.compareTo(c3));
        
    }

}
class  Card implements Comparable<Card>{
    public int rank;
    public String suit;
     public Card(int rank,String suit){
         this.rank = rank;
         this.suit = suit;
     }

    @Override
    public int compareTo(Card o) {
        if(o==null){
            return 1;
        }
        return rank-o.rank;
    }
}

public interface Comparator<T> {
    /**
     * Compares its two arguments for order.  Returns a negative integer,
     * zero, or a positive integer as the first argument is less than, equal
     * to, or greater than the second.<p>
     *
     * In the foregoing description, the notation
     * <tt>sgn(</tt><i>expression</i><tt>)</tt> designates the mathematical
     * <i>signum</i> function, which is defined to return one of <tt>-1</tt>,
     * <tt>0</tt>, or <tt>1</tt> according to whether the value of
     * <i>expression</i> is negative, zero or positive.<p>
     *
     * The implementor must ensure that <tt>sgn(compare(x, y)) ==
     * -sgn(compare(y, x))</tt> for all <tt>x</tt> and <tt>y</tt>.  (This
     * implies that <tt>compare(x, y)</tt> must throw an exception if and only
     * if <tt>compare(y, x)</tt> throws an exception.)<p>
     *
     * The implementor must also ensure that the relation is transitive:
     * <tt>((compare(x, y)&gt;0) &amp;&amp; (compare(y, z)&gt;0))</tt> implies
     * <tt>compare(x, z)&gt;0</tt>.<p>
     *
     * Finally, the implementor must ensure that <tt>compare(x, y)==0</tt>
     * implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all
     * <tt>z</tt>.<p>
     *
     * It is generally the case, but <i>not</i> strictly required that
     * <tt>(compare(x, y)==0) == (x.equals(y))</tt>.  Generally speaking,
     * any comparator that violates this condition should clearly indicate
     * this fact.  The recommended language is "Note: this comparator
     * imposes orderings that are inconsistent with equals."
     *
     * @param o1 the first object to be compared.
     * @param o2 the second object to be compared.
     * @return a negative integer, zero, or a positive integer as the
     *         first argument is less than, equal to, or greater than the
     *         second.
     * @throws NullPointerException if an argument is null and this
     *         comparator does not permit null arguments
     * @throws ClassCastException if the arguments' types prevent them from
     *         being compared by this comparator.
     */
    int compare(T o1, T o2);

// write your code here
import java.util.*;
import java.lang.*;

public class Main{
    public static void main(String[] args){
        Card c1 = new Card(1,"♠");
        Card c2 = new Card(2,"♠");
        Card c3 = c1;
        CardComparator cardComparator = new CardComparator();
        System.out.println(cardComparator.compare(c1,c2));
        System.out.println(cardComparator.compare(c1,c3));
        System.out.println(cardComparator.compare(c2,c3));
    }
}
class  Card {
    public int rank;
    public String suit;
     public Card(int rank,String suit){
         this.rank = rank;
         this.suit = suit;
     }
}
class  CardComparator implements Comparator<Card>{

    @Override
    public int compare(Card o1, Card o2) {
        if (o1==o2){
            return 0;
        }
        if (o1==null)return -1;
        if (o2==null)return 1;
        return o1.rank-o2.rank;
    }
}