Java技巧积累

写文件

        try {
            PrintWriter pw = new PrintWriter(new File(filepath));
            pw.write("test\n");
            pw.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

读文件

        Scanner sc = new Scanner(new File(typeFilePath));
        while (sc.hasNextLine()) {
            String line = sc.nextLine().trim();
        }

PriorityQueue，使用Comparator

来自GeekForGeeks

// Java program to demonstrate working of 
// comparator based priority queue constructor
import java.util.*;
 
public class Example {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        // Creating Priority queue constructor having 
        // initial capacity=3 and a StudentComparator instance 
        // as its parameters
        PriorityQueue<Student> pq = new
             PriorityQueue<Student>(5, new StudentComparator());
                 
                // Invoking a parameterized Student constructor with 
                // name and cgpa as the elements of queue
                Student student1 = new Student("Nandini", 3.2);
                 
                // Adding a student object containing fields 
                // name and cgpa to priority queue 
                pq.add(student1);
                Student student2 = new Student("Anmol", 3.6);
                        pq.add(student2);         
                Student student3 = new Student("Palak", 4.0);
                        pq.add(student3);
                 
                // Printing names of students in priority order,poll()
                // method is used to access the head element of queue
                System.out.println("Students served in their priority order");
                 
                while (!pq.isEmpty()) {
                System.out.println(pq.poll().getName());
        } 
    }
} 
 
class StudentComparator implements Comparator<Student>{
             
            // Overriding compare()method of Comparator 
                        // for descending order of cgpa
            public int compare(Student s1, Student s2) {
                if (s1.cgpa < s2.cgpa)
                    return 1;
                else if (s1.cgpa > s2.cgpa)
                    return -1;
                                return 0;
                }
        }
 
class Student {
    public String name;
    public double cgpa;
         
    // A parameterized student constructor
    public Student(String name, double cgpa) {
     
        this.name = name;
        this.cgpa = cgpa;
    }
     
    public String getName() {
        return name;
    } 
}