有人可以向我解释如何使用Collections.sort()按姓氏对列表进行排序并显示排序列表。然后编写第二个实现Comparator的内部类，并覆盖compare()方法，允许对size实例变量进行比较。
public Animal(){
fname = "unknown";
lname = "unknown";
size = 0;
}
public Animal(String fname, String lname, int size) {
this.fname = fname;
this.lname = lname;
this.size = size;
}
//getters and setters
public String getFName(){
return fname;
}
public void setFName(String fname){
this.fname = fname;
}
public String getLName(){
return lname;
}
public void setLName(String lname){
this.lname = lname;
}
public int getSize(){
return size;
}
public void setSize(int size){
this.size = size;
}
//compare by fname
public int compareTo(Animal lname) {
return fname.compareTo(lname.fname);
}
//sound method
abstract String sound();
//toString method
@Override
public String toString(){
return getFName() + " " + getLName() + " " + sound() + " " + getSize();
}
}//end class
public class AnimalTester {
//inner class implementing comparable
static abstract class InnerClass implements Comparable<Animal>{
private static final String lname = "Not Given";
List<Animal> dogList2 = new LinkedList<Animal>();
List<Animal> catList2 = new LinkedList<Animal>();
//override compareto and compare lname
int dogListCompare = InnerClass.lname.compareTo(((Animal) dogList2).getLName());
int catListCompare = InnerClass.lname.compareTo(((Animal) catList2).getLName());
}//end inner class
public static void main(String[] args){
String fileName = "animal.dat";
Scanner input = new Scanner(System.in);
//create LinkedList
List<Dog> dogList = new LinkedList<Dog>();
List<Cat> catList = new LinkedList<Cat>();
List<Dog> dogList2 = new LinkedList<Dog>();
List<Cat> catList2 = new LinkedList<Cat>();
String fname;
String lname;
//String yes = "y";
char yes = 'y';
int x = 0;
//while(yes.equals("y")){
while(yes == 'y' || yes == 'Y'){
//declare & create a Dog & Cat object
dogList.add(new Dog());
System.out.print("First Name (dog): ");
fname = input.next();
System.out.print("Last Name (dog): ");
lname = input.next();
dogList2.add(new Dog());
System.out.print("First Name Again (dog): ");
fname = input.next();
System.out.print("Last Name Again (dog): ");
lname = input.next();
System.out.println(" "); //line break
catList.add(new Cat());
System.out.print("First Name (cat): ");
fname = input.next();
System.out.print("Last Name (cat): ");
lname = input.next();
catList2.add(new Cat());
System.out.print("First Name Again (cat): ");
fname = input.next();
System.out.print("Last Name Again (cat): ");
lname = input.next();
dogList.get(x).setFName(fname);
dogList.get(x).setLName(lname);
catList.get(x).setFName(fname);
catList.get(x).setLName(lname);
dogList2.get(x).setFName(fname);
dogList2.get(x).setLName(lname);
catList2.get(x).setFName(fname);
catList2.get(x).setLName(lname);
x++; //increment x
System.out.print("Continue? [y/n]: ");
System.out.println(" ");
yes = input.next().charAt(0);
}//end while
System.out.println("");
//enhanced for loops
for(Dog element:dogList){
System.out.println(element.toString());
}
for(Dog element:dogList2){
System.out.println(element.toString());
}
for(Cat element:catList2){
System.out.println(element.toString());
}
for(Cat element:catList){
System.out.println(element.toString());
}
//sort lists by fname
Collections.sort(dogList, new Comparator<Animal>() {
public int compare(Animal one, Animal fname) {
return one.getFName().compareTo(fname.getLName());
}
});
Collections.sort(catList, new Comparator<Animal>() {
public int compare(Animal one, Animal fname) {
return one.getFName().compareTo(fname.getLName());
}
});
//sort lists by lname
Collections.sort(dogList2, new Comparator<Animal>() {
public int compare(Animal two, Animal lname) {
return two.getLName().compareTo(lname.getFName());
}
});
Collections.sort(catList2, new Comparator<Animal>() {
public int compare(Animal two, Animal lname) {
return two.getLName().compareTo(lname.getFName());
}
});
//display lists
System.out.println(" ");
System.out.println("Initial List ON FName: "+dogList);
Collections.sort(dogList);
System.out.println("Sorted List ON FName: "+dogList);
System.out.println(" ");
System.out.println("Initial List ON FName: "+catList);
Collections.sort(catList);
System.out.println("Sorted List ON FName: "+catList);
System.out.println(" ");
System.out.println("Initial List ON LName: "+dogList2);
Collections.sort(dogList2);
System.out.println("Sorted List ON LName: "+dogList2);
System.out.println(" ");
System.out.println("Initial List ON LName: "+catList2);
Collections.sort(catList2);
System.out.println("Sorted List ON LName: "+catList2);
}//end main
}//end class
我需要有3组按名字，名字和大小排序的列表。我用第一个和第二个名字尝试了一切，我不能这样做......
答案 0 :(得分：0)
快速建议，而不是InnerClass实施Comparable<Animal>，您希望它实施Comparator<Animal>。 Comparable<T>表示此对象可与T进行比较，Comparator<T>表示此对象可以比较两个T。
查看Oracle's tutorial on Object Ordering，它实际上非常有用。
答案 1 :(得分：0)
最好使用comparator来排序具有不同条件的相同bean。
以下是一个示例代码：
Dog.class：
public class Dog extends Animal {
public Dog(String fname, String lname, int size) {
super(fname, lname, size);
}
@Override
String sound() {
return "bark";
}
}
猫类：
public class Cat extends Animal {
public Cat(String fname, String lname, int size) {
super(fname, lname, size);
}
@Override
String sound() {
return "meauvvv";
}
}
Animal.class：
public abstract class Animal {
private String fname;
private String lname;
private int size;
public Animal(String fname, String lname, int size) {
this.fname = fname;
this.lname = lname;
this.size = size;
}
//getters and setters
public String getFName(){
return fname;
}
public void setFName(String fname){
this.fname = fname;
}
public String getLName(){
return lname;
}
public void setLName(String lname){
this.lname = lname;
}
public int getSize(){
return size;
}
public void setSize(int size){
this.size = size;
}
//compare by fname
public int compareTo(Animal lname) {
return fname.compareTo(lname.fname);
}
//sound method
abstract String sound();
//toString method
@Override
public String toString(){
return getFName() + " " + getLName() + " " + sound() + " " + getSize();
}
}
DogCatComparator.class：
public class DogCatComparator implements Comparator<Animal> {
@Override
public int compare(Animal arg0, Animal arg1) {
//null checks here
if(arg0.sound().equals(arg1.sound())){
return 0;
}
if(arg0.sound().equals("bark") && arg1.sound().equals("meauvvv")){
return -1;
}
return 1;
}
}
NameComparator.class：
public class NameComparator implements Comparator<Animal> {
@Override
public int compare(Animal arg0, Animal arg1) {
//null check here
return arg0.getFName().compareTo(arg1.getFName());
}
}
SizeComparator.class：
public class SizeComparator implements Comparator<Animal> {
@Override
public int compare(Animal arg0, Animal arg1) {
//null check here
if(arg0.getSize() == arg1.getSize()){
return 0;
}
return arg0.getSize() > arg1.getSize() ? 1 : -1;
}
}
示例：
public class Main {
public static void main(String[] args) {
Dog dog1 = new Dog("dog1Name", "dog1lname", 5);
Dog dog2 = new Dog("dog2Name", "dog2lname", 3);
Cat cat1 = new Cat("cat1Name", "cat1lname", 7);
Cat cat2 = new Cat("cat2Name", "cat2lname", 1);
List<Animal> animals = new LinkedList<>();
animals.add(cat2);
animals.add(cat1);
animals.add(dog2);
animals.add(dog1);
Collections.sort(animals, new DogCatComparator());
printList(animals);
Collections.sort(animals, new SizeComparator());
printList(animals);
Collections.sort(animals, new NameComparator());
printList(animals);
}
private static void printList(List<Animal> animals){
System.out.println("-------------");
for(Animal animal: animals){
System.out.println(animal.toString());
}
}
}
结果：
-------------
dog2Name dog2lname bark 3
dog1Name dog1lname bark 5
cat2Name cat2lname meauvvv 1
cat1Name cat1lname meauvvv 7
-------------
cat2Name cat2lname meauvvv 1
dog2Name dog2lname bark 3
dog1Name dog1lname bark 5
cat1Name cat1lname meauvvv 7
-------------
cat1Name cat1lname meauvvv 7
cat2Name cat2lname meauvvv 1
dog1Name dog1lname bark 5
dog2Name dog2lname bark 3