JAVA对象比较器Comparator

排序的算法是我们最常用的算法，初学程序，每个人都尝试过排序。但只是局限于简单的排序。
如将下列数字进行排序
1，3，5，8，3，6
于是我们得出结果
1，3，3，5，6，8
将下列字母（字符）进行排序
a,i,e,f,w,s
于是我们得出结果
a,e,f,i,s,w
但是我们遇到的情况就不是如此简单了。如给公司里的商品进行排序，我们很轻易的想到按照商品的名称排序不就完了，而且简单明了。但现实并如我们相信般简单。同一商品名称可以有不同的批次，进货时间，可能还会有单价的不同。显然只根据商品名称排序是不合理的。

再举个简单例子然后用程序实现。如公司要将员工进行排序（不要说领导排在前面），假设我们的需求比较复杂。先进行姓排序，谁的姓拼音靠前，谁就排前面。然后对名字进行排序。恩.如果同名，女性排前头。如果名字和性别都相同，年龄小的排前头。ok，一个也不算复杂的需求。

如果对java比较熟悉的会知道java.util.Comparator 接口。要实现里面的函数
int compare(Object o1, Object o2) 返回一个基本类型的整型，返回负数表示o1 小于o2，返回0 表示o1和o2相等，返回正数表示o1大于o2。

于是我们设计的人员类要有几个变量，firstname,lastname,sex,age分别表示姓，名，性别，年龄。

public class Person {
String firstname,lastname;
Boolean sex;
Integer age;
public Person(String firstname,String lastname,Boolean sex,Integer age) {
    this.firstname = firstname;
    this.lastname = lastname;
    this.sex = sex;
    this.age = age;
}
public String getFirstName() {
     return firstname;
   }

   public String getLastName() {
     return lastname;
   }
   public Boolean getSex() {
      return sex;
    }

    public Integer getAge() {
      return age;
    }

//为了输入方便，重写了toString()
public String toString()
    {
      return firstname +" "+lastname+" "+(sex.booleanValue()?"男":"女")+" "+age;
    }
}
//end person

public class Person {
String firstname,lastname;
Boolean sex;
Integer age;
public Person(String firstname,String lastname,Boolean sex,Integer age) {
    this.firstname = firstname;
    this.lastname = lastname;
    this.sex = sex;
    this.age = age;
}
public String getFirstName() {
     return firstname;
   }

   public String getLastName() {
     return lastname;
   }
   public Boolean getSex() {
      return sex;
    }

    public Integer getAge() {
      return age;
    }

//为了输入方便，重写了toString()
public String toString()
    {
      return firstname +" "+lastname+" "+(sex.booleanValue()?"男":"女")+" "+age;
    }
}
//end person

下面是要实现比较器

public class Comparators {
public static java.util.Comparator getComparator() {
    return new java.util.Comparator() {

      public int compare(Object o1, Object o2) {
        if (o1 instanceof String) {
          return compare( (String) o1, (String) o2);
        }else if (o1 instanceof Integer) {
          return compare( (Integer) o1, (Integer) o2);
        }else if (o1 instanceof Person) {
        return compare( (Person) o1, (Person) o2);
        }else {
          System.err.println("未找到合适的比较器");
          return 1;

        }
      }

      public int compare(String o1, String o2) {
        String s1 = (String) o1;
        String s2 = (String) o2;
        int len1 = s1.length();
        int len2 = s2.length();
        int n = Math.min(len1, len2);
        char v1[] = s1.toCharArray();
        char v2[] = s2.toCharArray();
        int pos = 0;

        while (n-- != 0) {
          char c1 = v1[pos];
          char c2 = v2[pos];
          if (c1 != c2) {
            return c1 - c2;
          }
          pos++;
        }
        return len1 - len2;
      }

      public int compare(Integer o1, Integer o2) {
        int val1 = o1.intValue();
        int val2 = o2.intValue();
        return (val1 < val2 ? -1 : (val1 == val2 ? 0 : 1));

      }
      public int compare(Boolean o1, Boolean o2) {

         return (o1.equals(o2)? 0 : (o1.booleanValue()==true?1:-1));

       }

      public int compare(Person o1, Person o2) {
        String firstname1 = o1.getFirstName();
        String firstname2 = o2.getFirstName();
        String lastname1 = o1.getLastName();
        String lastname2 = o2.getLastName();
        Boolean sex1 = o1.getSex();
        Boolean sex2 = o2.getSex();
        Integer age1 = o1.getAge();
        Integer age2 = o2.getAge();
        return (compare(firstname1, firstname2) == 0 ?
             (compare(lastname1, lastname2) == 0 ? (compare(sex1, sex2) == 0 ? (compare(age1, age2) == 0 ? 0 :
              compare(age1, age2)) :
              compare(sex1, sex2)) :
              compare(lastname1, lastname2)) :
              compare(firstname1, firstname2));

      }

    };
}

}

public class Comparators {
public static java.util.Comparator getComparator() {
    return new java.util.Comparator() {

      public int compare(Object o1, Object o2) {
        if (o1 instanceof String) {
          return compare( (String) o1, (String) o2);
        }else if (o1 instanceof Integer) {
          return compare( (Integer) o1, (Integer) o2);
        }else if (o1 instanceof Person) {
        return compare( (Person) o1, (Person) o2);
        }else {
          System.err.println("未找到合适的比较器");
          return 1;

        }
      }

      public int compare(String o1, String o2) {
        String s1 = (String) o1;
        String s2 = (String) o2;
        int len1 = s1.length();
        int len2 = s2.length();
        int n = Math.min(len1, len2);
        char v1[] = s1.toCharArray();
        char v2[] = s2.toCharArray();
        int pos = 0;

        while (n-- != 0) {
          char c1 = v1[pos];
          char c2 = v2[pos];
          if (c1 != c2) {
            return c1 - c2;
          }
          pos++;
        }
        return len1 - len2;
      }

      public int compare(Integer o1, Integer o2) {
        int val1 = o1.intValue();
        int val2 = o2.intValue();
        return (val1 < val2 ? -1 : (val1 == val2 ? 0 : 1));

      }
      public int compare(Boolean o1, Boolean o2) {

         return (o1.equals(o2)? 0 : (o1.booleanValue()==true?1:-1));

       }

      public int compare(Person o1, Person o2) {
        String firstname1 = o1.getFirstName();
        String firstname2 = o2.getFirstName();
        String lastname1 = o1.getLastName();
        String lastname2 = o2.getLastName();
        Boolean sex1 = o1.getSex();
        Boolean sex2 = o2.getSex();
        Integer age1 = o1.getAge();
        Integer age2 = o2.getAge();
        return (compare(firstname1, firstname2) == 0 ?
             (compare(lastname1, lastname2) == 0 ? (compare(sex1, sex2) == 0 ? (compare(age1, age2) == 0 ? 0 :
              compare(age1, age2)) :
              compare(sex1, sex2)) :
              compare(lastname1, lastname2)) :
              compare(firstname1, firstname2));

      }

    };
}

}

以上代码有可能因为浏览器的布局自动换行。
compare(Person o1, Person o2)的返回值看起来比较别扭。最简单的是

public int compare(Boolean o1, Boolean o2) {

     return (o1.equals(o2)? 0 : (o1.booleanValue()==true?1:-1));

 }

    public int compare(Boolean o1, Boolean o2) {

         return (o1.equals(o2)? 0 : (o1.booleanValue()==true?1:-1));

     }

o1和o2相等返回0，否则o1如果是true 就表示o1大于o2。

再尝试输出结果看看

public class Main {
public Main() {
}
public static void main(String[] args) {
    Person[] person = new Person[] {
         new Person("ouyang", "feng", Boolean.TRUE, new Integer(27)),
         new Person("zhuang", "gw", Boolean.TRUE, new Integer(27)),
         new Person("zhuang", "gw", Boolean.FALSE, new Integer(27)),
         new text.Person("zhuang", "gw", Boolean.FALSE, new Integer(2)),


     };
     for (int i = 0; i < person.length; i++) {
       System.out.println("before sort=" + person[i]);
     }
     java.util.Arrays.sort(person, Comparators.getComparator());

     for (int i = 0; i < person.length; i++) {
        System.out.println("after sort=" + person[i]);
     }


}

}

public class Main {
public Main() {
}
public static void main(String[] args) {
    Person[] person = new Person[] {
         new Person("ouyang", "feng", Boolean.TRUE, new Integer(27)),
         new Person("zhuang", "gw", Boolean.TRUE, new Integer(27)),
         new Person("zhuang", "gw", Boolean.FALSE, new Integer(27)),
         new text.Person("zhuang", "gw", Boolean.FALSE, new Integer(2)),


     };
     for (int i = 0; i < person.length; i++) {
       System.out.println("before sort=" + person[i]);
     }
     java.util.Arrays.sort(person, Comparators.getComparator());

     for (int i = 0; i < person.length; i++) {
        System.out.println("after sort=" + person[i]);
     }


}

}

输出结果：

before sort=ouyang feng 男 27

before sort=zhuang gw 男 27

before sort=zhuang gw 女 27

before sort=zhuang gw 女 2

after sort=ouyang feng 男 27

after sort=zhuang gw 女 2

after sort=zhuang gw 女 27

after sort=zhuang gw 男 27

before sort=ouyang feng 男 27

before sort=zhuang gw 男 27

before sort=zhuang gw 女 27

before sort=zhuang gw 女 2

after sort=ouyang feng 男 27

after sort=zhuang gw 女 2

after sort=zhuang gw 女 27

after sort=zhuang gw 男 27

仔细理解java的Comparator会给你写排序带来很大帮助