【Java 基础】Comparable 接口的使用

leo 3年前 (2015-10-04) Java基础 | 抢沙发 198

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【Java 基础】Comparable 接口的使用

前几天有网友让解释一下CompareTo函数，今天在这里给大家讲一下。

CompareTo函数是Comparable接口的一个方法，Comparable接口源码如下：

public interface Comparable<T> {
   /**
    * Compares this object to the specified object to determine their relative
    * order.
    *
    * @param another
    *            the object to compare to this instance.
    * @return a negative integer if this instance is less than {@code another};
    *         a positive integer if this instance is greater than
    *         {@code another}; 0 if this instance has the same order as
    *         {@code another}.
    * @throws ClassCastException
    *             if {@code another} cannot be converted into something
    *             comparable to {@code this} instance.
    */
   int compareTo(T another);
}

public interface Comparable<T> {

/**

* Compares this object to the specified object to determine their relative

* order.

* @param another

* the object to compare to this instance.

* @return a negative integer if this instance is less than {@code another};

* a positive integer if this instance is greater than

* {@code another}; 0 if this instance has the same order as

* {@code another}.

* @throws ClassCastException

* if {@code another} cannot be converted into something

* comparable to {@code this} instance.

int compareTo(T another);

}

一个实现了Comparable接口的对象的实例可以被用于和相同对象的不同实例做对比，它本身必须实现java.lang.Comparable的接口，这样它就拥有了对比的能力。具体怎么做呢？看下面的代码。

public class Student implements Comparable<Student> {
   int age;
   String name;
   Student(int age, String name) {
       this.age = age;
       this.name = name;
   }
   @Override
   public String toString() {
       return " age = " + age + " name = " + name;
   }
   @Override
   public int compareTo(Student o) {
       return this.age - o.age;
   }
   public static void main(String[] arg) {
       ArrayList<Student> students = new ArrayList<Student>();
       students.add(new Student(23, "dd"));
       students.add(new Student(22, "cc"));
       students.add(new Student(22, "bb"));
       students.add(new Student(25, "aa"));
       Collections.sort(students);
       System.out.print(students);
   }
}