Writing our own Collection mechanism to Sort different objects in Java.

SortCollections.java

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        package com.ranga.collections;

        import java.lang.reflect.Field;
        import java.util.Collections;
        import java.util.Comparator;
        import java.util.List;

        public class SortCollections<T> {
            
            private List<T> collectionList;
            private String sortingField = null;
            private boolean isAscending = true; 

            public SortCollections(List<T> objectList, String sortField) {
                this(objectList, sortField, true);      
            }
            
            public SortCollections(List<T> collectionList, String sortField, boolean isAscending) {
                super();
                this.collectionList = collectionList;
                this.sortingField = sortField;
                this.isAscending = isAscending;
            }

            @SuppressWarnings("rawtypes")
            public List<T> sort( final Class claz) {
                final String sortingField = this.sortingField;      
                final Boolean isAscending = this.isAscending;
                
                Collections.sort(this.collectionList, new Comparator<T>() {
                    @Override
                    public int compare(T object1, T object2) {
                        try {
                            Field sortField = claz.getDeclaredField(sortingField);
                            sortField.setAccessible(true);

                            Object value1 = sortField.get(object1);
                            Object value2 = sortField.get(object2);

                            if (value1 instanceof String && value2 instanceof String) { // String field
                                String string1 = (String) value1;
                                String string2 = (String) value2;
                                if (true == isAscending) { 
                                    return string1.compareTo(string2);
                                } else {
                                    return string2.compareTo(string1);
                                }
                            } else { // Numeric field
                                Number number1 = (Number) value1;
                                Number number2 = (Number) value2;
                                if (true == isAscending) {
                                    if (number1.floatValue() > number2.floatValue()) {
                                        return 1;
                                    } else {
                                        return -1;
                                    }
                                } else {
                                    if (number2.floatValue() > number1.floatValue()) {
                                        return 1;
                                    } else {
                                        return -1;
                                    }
                                }
                            }
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                        return 0;
                    }
                });
                return this.collectionList;
            }
        }
    
Employee.java

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    package com.ranga.collections;
    import java.io.Serializable;    
    public class Employee implements Serializable {
        
        private int id;
        private String name;
        private int age;
        private float salary;
        
        public Employee() {
            super();        
        }
        
        public Employee(int id, String name, int age, float salary) {
            super();
            this.id = id;
            this.name = name;
            this.age = age;
            this.salary = salary;
        }

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            this.age = age;
        }

        public float getSalary() {
            return salary;
        }

        public void setSalary(float salary) {
            this.salary = salary;
        }

        @Override
        public String toString() {
            return "Employee [id=" + id + ", name=" + name + ", age=" + age
                    + ", salary=" + salary + "]";
        }
    }

Application.java
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    package com.ranga.collections;
    import java.util.ArrayList;
    import java.util.List;
    public class Application {
        public static void main(String[] args) {
            List<Employee> employees = new ArrayList<Employee>();
            employees.add(new Employee(1,"Ranga", 26, 25677 ));
            employees.add(new Employee(2,"Raja", 50, 2577 ));
            employees.add(new Employee(3,"Vasu", 20, 30677 ));
            employees.add(new Employee(4,"Mani", 45, 45677 ));
            employees.add(new Employee(5,"Yasu", 29, 67677 ));
            employees.add(new Employee(6,"Vinod", 80, 5677 ));
            
            System.out.println(employees);
            List<Employee> employeeList = new SortCollections<Employee>(employees, "name", false).sort(Employee.class);     
            System.out.println(employeeList);       
            
            employeeList = new SortCollections<Employee>(employees, "salary").sort(Employee.class);     
            System.out.println(employeeList);
        }
    }

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