Java的两种比较器用法：Comparable和Comparator

清疚 2022-03-19 16:41 293阅读 0赞

Java有两种比较器：Comparable和Comparator。Comparable称之为内部比较器，实体类实现该接口，重写compareTo方法；

Comparator称之为外部比较器，可以自定义比较器类，实现该接口，重写compare方法。Comparator使用起来比Comparable更加的灵活，方便。以下是两种比较器具体的使用实例：

**1、内部比较器Comparable示例**

import java.util.ArrayList;
    import java.util.Collections;
    import java.util.List;
    
    public class compareDemo {
    	/*
    	 * 内部比较器Comparable示例
    	 */
    	@SuppressWarnings("unchecked")
    	public static void main(String[] args) {
    		List<Student> studentList = new ArrayList<Student>();
    		Student s1 = new Student("tom", "男", 23);
    		Student s2 = new Student("Jon", "男", 22);		
    		Student s3 = new Student("Quy", "男", 20);
    		Student s4 = new Student("Weg", "男", 21);
    		Student s5 = new Student("Kiy", "女", 20);
    		studentList.add(s1);
    		studentList.add(s2);
    		studentList.add(s3);
    		studentList.add(s4);
    		studentList.add(s5);
    		System.out.println("排序前："+studentList);
    		Collections.sort(studentList);
    		System.out.println("排序后："+studentList);
    	}
    }
    
    @SuppressWarnings({"rawtypes","unused"})
    class Student implements Comparable {
    	private String name;
    	private String gender;
    	private int age;
    
    	public Student(String name, String gender, int age) {
    		super();
    		this.name = name;
    		this.gender = gender;
    		this.age = age;
    	}
    	
    	@Override
    	public String toString() {
    		return "Student [name=" + name + ", gender=" + gender + ", age=" + age + "]";
    	}
    
    	/*
    	 * (non-Javadoc)先按照年龄比较，再按照姓名比较
    	 * @see java.lang.Comparable#compareTo(java.lang.Object)
    	 */
    	@Override
    	public int compareTo(Object object) {
    		int compareResult = 0;
    		Student student = (Student)object;
    		compareResult = age > student.age ? 1 : (age == student.age ? 0 : -1);
    		if(compareResult == 0) {
    			compareResult = name.charAt(0) > student.name.charAt(0) ? 1 : (name.charAt(0) == student.name.charAt(0) ? 0 : -1);
    		}
    		return compareResult;
    	}
    	
    }

**1、外部比较器Comparator示例**

Comparator有两种用法，一种是提前自定义比较器类，二种是使用内名内部类。具体示例如下：

import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Comparator;
    import java.util.List;
    
    public class compareDemo {
    	/*
    	 * 外部比较器Comparator示例
    	 */
    	@SuppressWarnings({ "unchecked", "rawtypes" })
    	public static void main(String[] args) {
    		List<Student> studentList = new ArrayList<Student>();
    		Student s1 = new Student("tom", "男", 23);
    		Student s2 = new Student("Jon", "男", 22);		
    		Student s3 = new Student("Quy", "男", 20);
    		Student s4 = new Student("Weg", "女", 21);
    		Student s5 = new Student("Kiy", "女", 20);
    		studentList.add(s1);
    		studentList.add(s2);
    		studentList.add(s3);
    		studentList.add(s4);
    		studentList.add(s5);
    		//1、使用方法1：自定义外部比较器类
    		System.out.println("使用方法1排序前："+studentList);
    		Collections.sort(studentList,new StudentCompare());
    		System.out.println("使用方法1排序后："+studentList);
    		studentList.clear();
    		studentList.add(s1);
    		studentList.add(s2);
    		studentList.add(s3);
    		studentList.add(s4);
    		studentList.add(s5);
    		//2、使用方法2：采用匿名内部类
    		System.out.println("使用方法2排序前："+studentList);
    		Collections.sort(studentList,new Comparator() {
    			@Override
    			public int compare(Object object1, Object object2) {
    				int compareResult = 0;
    				Student stu1 = (Student)object1;
    				Student stu2 = (Student)object2;
    				compareResult = stu1.gender.charAt(0) > stu2.gender.charAt(0) ? 1 : (stu1.gender.charAt(0) == stu2.gender.charAt(0) ? 0 : -1);
    				if(compareResult == 0) {		
    					compareResult = stu1.age > stu2.age ? 1 : (stu1.age == stu2.age ? 0 : -1);
    				}
    				if(compareResult == 0) {
    					compareResult = stu1.name.charAt(0) > stu2.name.charAt(0) ? 1 : (stu1.name.charAt(0) == stu2.name.charAt(0) ? 0 : -1);
    				}
    				return compareResult;
    			}
    		});	
    		System.out.println("使用方法2排序后："+studentList);
    	}
    }
    
    /**
     * 外部比较器Comparator:先按照性别比较，再按照年龄比较，再按照姓名比较
     */
    @SuppressWarnings("rawtypes")
    class StudentCompare implements Comparator {
    
    	@Override
    	public int compare(Object object1, Object object2) {
    		int compareResult = 0;
    		Student stu1 = (Student)object1;
    		Student stu2 = (Student)object2;
    		compareResult = stu1.gender.charAt(0) > stu2.gender.charAt(0) ? 1 : (stu1.gender.charAt(0) == stu2.gender.charAt(0) ? 0 : -1);
    		if(compareResult == 0) {		
    			compareResult = stu1.age > stu2.age ? 1 : (stu1.age == stu2.age ? 0 : -1);
    		}
    		if(compareResult == 0) {
    			compareResult = stu1.name.charAt(0) > stu2.name.charAt(0) ? 1 : (stu1.name.charAt(0) == stu2.name.charAt(0) ? 0 : -1);
    		}
    		return compareResult;
    	}	
    }
    
    @SuppressWarnings({"rawtypes","unused"})
    class Student implements Comparable {
    	public String name;
    	public String gender;
    	public int age;
    
    	public Student(String name, String gender, int age) {
    		super();
    		this.name = name;
    		this.gender = gender;
    		this.age = age;
    	}
    	
    	@Override
    	public String toString() {
    		return "Student [name=" + name + ", gender=" + gender + ", age=" + age + "]";
    	}
    
    	/*
    	 * (non-Javadoc)先按照年龄比较，再按照姓名比较
    	 * @see java.lang.Comparable#compareTo(java.lang.Object)
    	 */
    	@Override
    	public int compareTo(Object object) {
    		int compareResult = 0;
    		Student student = (Student)object;
    		compareResult = age > student.age ? 1 : (age == student.age ? 0 : -1);
    		if(compareResult == 0) {
    			compareResult = name.charAt(0) > student.name.charAt(0) ? 1 : (name.charAt(0) == student.name.charAt(0) ? 0 : -1);
    		}
    		return compareResult;
    	}
    }