Example of creating inner classes and using comparators

Code

// https://projectlombok.org/features/Data.html
// @Data generates all the boilerplate that is normally associated with simple POJOs (Plain Old Java Objects) and beans: 
// getters for all fields, setters for all non-final fields, and appropriate toString, equals and hashCode
@Data
public static class Student {
	private final String name;
	private final int grade;
}

public static class GradeComparator implements Comparator<Student> {
	@Override public int compare(Student o1, Student o2) {
		// descending order (ascending order would be: o1.getGrade()-o2.getGrade())
		return o2.getGrade() - o1.getGrade();
	}
}

public static void main(String args[]) {
	
	List<Student> students = new ArrayList<>();
	students.add(new Student("Jim", 22));
	students.add(new Student("Elizabeth", 19));
	students.add(new Student("Bob", 30));

	Dump(students, "Order of students before sorting is: ");

	Collections.sort(students, new GradeComparator());
	Dump(students, "Order of students after sorting by student grade is");

	Collections.sort(students, (Student r, Student s) -> r.getName().compareTo(s.getName()));
	Dump(students, "Order of students after sorting by student name is");
}

Result

Console

Order of students before sorting is:  => [RunnContainer.Student(name=Jim, grade=22), RunnContainer.Student(name=Elizabeth, grade=19), RunnContainer.Student(name=Bob, grade=30)]
Order of students after sorting by student grade is => [RunnContainer.Student(name=Bob, grade=30), RunnContainer.Student(name=Jim, grade=22), RunnContainer.Student(name=Elizabeth, grade=19)]
Order of students after sorting by student name is => [RunnContainer.Student(name=Bob, grade=30), RunnContainer.Student(name=Elizabeth, grade=19), RunnContainer.Student(name=Jim, grade=22)]

Bytecode

Compiled from "RunnContainer.java"
public class io.jpad.scratch.RunnContainer {
  public io.jpad.scratch.RunnContainer();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: new           #2                  // class java/util/ArrayList
       3: dup
       4: invokespecial #3                  // Method java/util/ArrayList."<init>":()V
       7: astore_1
       8: aload_1
       9: new           #4                  // class io/jpad/scratch/RunnContainer$Student
      12: dup
      13: ldc           #5                  // String Jim
      15: bipush        22
      17: invokespecial #6                  // Method io/jpad/scratch/RunnContainer$Student."<init>":(Ljava/lang/String;I)V
      20: invokeinterface #7,  2            // InterfaceMethod java/util/List.add:(Ljava/lang/Object;)Z
      25: pop
      26: aload_1
      27: new           #4                  // class io/jpad/scratch/RunnContainer$Student
      30: dup
      31: ldc           #8                  // String Elizabeth
      33: bipush        19
      35: invokespecial #6                  // Method io/jpad/scratch/RunnContainer$Student."<init>":(Ljava/lang/String;I)V
      38: invokeinterface #7,  2            // InterfaceMethod java/util/List.add:(Ljava/lang/Object;)Z
      43: pop
      44: aload_1
      45: new           #4                  // class io/jpad/scratch/RunnContainer$Student
      48: dup
      49: ldc           #9                  // String Bob
      51: bipush        30
      53: invokespecial #6                  // Method io/jpad/scratch/RunnContainer$Student."<init>":(Ljava/lang/String;I)V
      56: invokeinterface #7,  2            // InterfaceMethod java/util/List.add:(Ljava/lang/Object;)Z
      61: pop
      62: aload_1
      63: ldc           #10                 // String Order of students before sorting is:
      65: invokestatic  #11                 // Method io/jpad/scratch/Dumper.Dump:(Ljava/lang/Object;Ljava/lang/String;)Ljava/lang/Object;
      68: pop
      69: aload_1
      70: new           #12                 // class io/jpad/scratch/RunnContainer$GradeComparator
      73: dup
      74: invokespecial #13                 // Method io/jpad/scratch/RunnContainer$GradeComparator."<init>":()V
      77: invokestatic  #14                 // Method java/util/Collections.sort:(Ljava/util/List;Ljava/util/Comparator;)V
      80: aload_1
      81: ldc           #15                 // String Order of students after sorting by student grade is
      83: invokestatic  #11                 // Method io/jpad/scratch/Dumper.Dump:(Ljava/lang/Object;Ljava/lang/String;)Ljava/lang/Object;
      86: pop
      87: aload_1
      88: invokedynamic #16,  0             // InvokeDynamic #0:compare:()Ljava/util/Comparator;
      93: invokestatic  #14                 // Method java/util/Collections.sort:(Ljava/util/List;Ljava/util/Comparator;)V
      96: aload_1
      97: ldc           #17                 // String Order of students after sorting by student name is
      99: invokestatic  #11                 // Method io/jpad/scratch/Dumper.Dump:(Ljava/lang/Object;Ljava/lang/String;)Ljava/lang/Object;
     102: pop
     103: return

  private static int lambda$main$0(io.jpad.scratch.RunnContainer$Student, io.jpad.scratch.RunnContainer$Student);
    Code:
       0: aload_0
       1: invokevirtual #18                 // Method io/jpad/scratch/RunnContainer$Student.getName:()Ljava/lang/String;
       4: aload_1
       5: invokevirtual #18                 // Method io/jpad/scratch/RunnContainer$Student.getName:()Ljava/lang/String;
       8: invokevirtual #19                 // Method java/lang/String.compareTo:(Ljava/lang/String;)I
      11: ireturn
}

Jpad Version:1.04

viewCount:7923

Creator: admin

Latest Editor: admin

Tags

Download

Copy As Markdown:

**code [Example of creating inner classes and using comparators.java](/example/1m/example-of-creating-inner-classes-and-using-comparators)**

// https://projectlombok.org/features/Data.html
    // @Data generates all the boilerplate that is normally associated with simple POJOs (Plain Old Java Objects) and beans: 
    // getters for all fields, setters for all non-final fields, and appropriate toString, equals and hashCode
    @Data
    public static class Student {
    	private final String name;
    	private final int grade;
    }
    
    public static class GradeComparator implements Comparator<Student> {
    	@Override public int compare(Student o1, Student o2) {
    		// descending order (ascending order would be: o1.getGrade()-o2.getGrade())
    		return o2.getGrade() - o1.getGrade();
    	}
    }
    
    public static void main(String args[]) {
    	
    	List<Student> students = new ArrayList<>();
    	students.add(new Student("Jim", 22));
    	students.add(new Student("Elizabeth", 19));
    	students.add(new Student("Bob", 30));
    
    	Dump(students, "Order of students before sorting is: ");
    
    	Collections.sort(students, new GradeComparator());
    	Dump(students, "Order of students after sorting by student grade is");
    
    	Collections.sort(students, (Student r, Student s) -> r.getName().compareTo(s.getName()));
    	Dump(students, "Order of students after sorting by student name is");
    }
**Result:**

Order of students before sorting is:  => [RunnContainer.Student(name=Jim, grade=22), RunnContainer.Student(name=Elizabeth, grade=19), RunnContainer.Student(name=Bob, grade=30)]
    Order of students after sorting by student grade is => [RunnContainer.Student(name=Bob, grade=30), RunnContainer.Student(name=Jim, grade=22), RunnContainer.Student(name=Elizabeth, grade=19)]
    Order of students after sorting by student name is => [RunnContainer.Student(name=Bob, grade=30), RunnContainer.Student(name=Elizabeth, grade=19), RunnContainer.Student(name=Jim, grade=22)]