java基础总结4

Posted 2020-06-23 黄小鱼ZZZ

Collections工具类
     是java集合框架中，用来操作集合对象的工具类
     也是java集合框架的成员
     sort（）排序方法
     Collections。sort()
     List<Integer>
     List<包装类>
     List<String>
Comparable & Comparator简介
     Comparable接口，是可比较的
     实现该接口表示：这个类的实例可以比较大小，可以进行自然排序
     定义了默认的比较规则
     其实现类需实现compareTo()方法
     compareTo()方法返回正数表示大，负数表示小，0表示相等
     Comparator接口比较工具接口
     用于定义临时比较规则，而不是默认比较规则
     其实现类需要实现compare()方法
     Comparator和Comparable都是java集合框架的成员

案例：

 public class Student implements Comparable<Student>{
       String id;
       String name;
	public Student(String ID, String st_Name) {
		// TODO Auto-generated constructor stub
		this.id = ID;
		this.name = st_Name;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	@Override
	public int compareTo(Student o) {
		// TODO Auto-generated method stub
		
		return this.id.compareTo(o.id);
	}
       
}

public class StudentComparator implements Comparator<Student> {

	@Override
	public int compare(Student arg0, Student arg1) {
		// TODO Auto-generated method stub
		return arg0.name.compareTo(arg1.name);
	}

}

public class CollectionTest {

	/**
	 * 通过Collections.sort()方法，对Integer泛型的List进行排序
	 * 
	 */
	public void testSort1(){
		List<Integer> integerList = new ArrayList<Integer>();
		Random random = new Random();
		Integer k;
		for(int i = 0; i < 10;i++){
			do{
				k = random.nextInt(100);
			}while(integerList.contains(k));
			integerList.add(k);
			System.out.println("成功添加整数：" +  k);
		}
		System.out.println("排序前--------------------");
		for (Integer integer : integerList) {
			System.out.println("元素：" + integer);
		}
		Collections.sort(integerList);
		System.out.println("排序后---------------------");
		for (Integer integer : integerList) {
			System.out.println("元素：" + integer);
		}
	}
	/*
	 *  对String泛型的List进行排序
	 *  
	 * */
	public void testSort2(){
		List<String> stringList = new ArrayList<String>();
		stringList.add("del");
		stringList.add("lenovo");
		stringList.add("ios");
		stringList.add("apple");
		System.out.println("排序前----------------");
		for(String string:stringList){
			System.out.println("元素：" + string);
		}
		Collections.sort(stringList);
		System.out.println("排序后------------------");
		for(String string:stringList){
			System.out.println("元素：" + string);
		}
		
	}
	/*
	 * 对其他类型的泛型List进行排序
	 * */
	public void testSort3(){
		List<Student> studentList = new ArrayList<Student>();
		Random random = new Random();
		studentList.add(new Student(random.nextInt(1000) + "","xiaoming"));
		studentList.add(new Student(random.nextInt(1000) + "","xiaohong"));
		studentList.add(new Student(random.nextInt(1000) + "","xiaobing"));
		studentList.add(new Student(random.nextInt(1000) + "","abcde"));
		System.out.println("排序前-------------");
		for (Student student : studentList) {
			System.out.println("学生：" + student.id + "   "+ student.name);
		}
		Collections.sort(studentList);
		System.out.println("排序后------------");
		for (Student student : studentList) {
			System.out.println("学生：" + student.id + "  "+ student.name);
		}
		Collections.sort(studentList,new StudentComparator());
		System.out.println("按照姓名排序后-------------");
		for (Student student : studentList) {
			System.out.println("学生：" + student.id + "  "+ student.name);
		}
	}
	public static void main(String[] args) {
		// TODO Auto-generated method stub
        CollectionTest ct = new CollectionTest();
//        ct.testSort1();
//        ct.testSort2();
        ct.testSort3();
	}

}