我正在尝试使用Java中的ArrayList按名称，颜色和权重对Fruit类的特征进行排序。在创建类Fruit的实例之前，名称，颜色和重量都以字符串形式从用户读入。然后我需要将Fruit对象添加到ArrayList，并按照我之前提到的顺序对它们进行排序。换句话说，首先按字母顺序按名称，然后根据颜色，最后按重量。
我不完全确定如何从ArrayList类实现sort（）方法。你有什么建议吗？或者也许任何教程可以建议我在哪里可以提高对sort（）和ArrayLists的理解？
代码如下。
谢谢！
import java.util.*;
/**creates instances of the Fruits class, and stores the
* resulting objects in an array which can be ordered
* firsting alphebetically by name, then by colour, and
* finally, in ascending order by weight
**/
public class Driver
{
public static void main(String[]args)
{
Scanner s = new Scanner(System.in);
int input = 0;
ArrayList fruitInfo = new ArrayList();
do
{
System.out.println("Enter option: (1) add fruit (2) quit:");
input = s.nextInt();
s.nextLine();
switch(input)
{
case 1:{
System.out.println("Enter name, colour and mass in kg separated by a `enter code here`space");
String in = s.nextLine();
String[] temp = in.split(" ");
//create a new instance of the fruit class and add it to the `enter code here`<ArrayList> {@link ArrayList}, fruitInfo
fruitInfo.add(new Fruit(temp[0], temp[1], temp[2]));
break;
}
case 2:{
break;
}
default: System.out.println("Input incorrect. Try again.");
}
}
while(input!=2);
}
}
/* Class Fruits
* a class modelled on the characteristics of fruit
* each fruit has a name, colour and mass, which are
* stored as <Strings>
**/
public class Fruit
{
private String name;
private String col;
private String kg;
/* Constructor
* constructs an instance of the Fruit class
* using user defined characteristics
**/
public Fruit(String name, String colour, String mass)
{
this.name=name;
col=colour;
mass=kg;
}
}
答案 0 :(得分：1)
让你的Fruit类实现Comparable并在
中实现你的比较逻辑public class Fruit implements Comparable<Fruit>
...
public int compareTo(Fruit otherFruit) {
... your compare logic here ....
}
}
然后您可以使用Collections.sort（myList）;
对列表进行排序答案 1 :(得分：1)
您应该实施比较器
public class FruitComparator implements Comparator<Fruit> {
@Override
public int compareTo(Fruit f1, MyObject f2) {
if(!f1.getName().equals(f2.getName())) return f1.getName().compareTo(f2.getName()));
if(!f1.getColor().equals(f2.getColor)) return f1.getColor().compareTo(f2.getColor()));
if(!f1.getWeight().equals(f2.getWeight())) return f1.getWeight().compareTo(f2.getWeight()));
}
}
现在，您可以将Collections.sort方法与新比较器一起使用：
Collections.sort(fruitInfo, new FruitComparator());
答案 2 :(得分：0)
尝试运行此代码。
import java.util.*;
/**
* creates instances of the Fruits class, and stores the resulting objects in an
* array which can be ordered firsting alphebetically by name, then by colour,
* and finally, in ascending order by weight
*
*/
public class Driver {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
int input = 0;
ArrayList<Fruit> fruitInfo = new ArrayList<>();
do {
System.out.println("Enter option: (1) add fruit (2) quit:");
input = s.nextInt();
s.nextLine();
switch (input) {
case 1: {
System.out.println("Enter name, colour and mass in kg separated by a `enter code here`space");
String in = s.nextLine();
String[] temp = in.split(" ");
//create a new instance of the fruit class and add it to the `enter code here`<ArrayList> {@link ArrayList}, fruitInfo
fruitInfo.add(new Fruit(temp[0], temp[1], temp[2]));
Collections.sort(fruitInfo);
break;
}
case 2: {
break;
}
default:
System.out.println("Input incorrect. Try again.");
}
} while (input != 2);
}
}
/* Class Fruits
* a class modelled on the characteristics of fruit
* each fruit has a name, colour and mass, which are
* stored as <Strings>
**/
class Fruit implements Comparable<Fruit> {
private String name;
private String col;
private String kg;
public int compareTo(Fruit otherFruit) {
int nameCmp = name.compareTo(otherFruit.name);
if (nameCmp != 0) {
return nameCmp;
}
int colCmp = name.compareTo(otherFruit.col);
if (colCmp != 0) {
return colCmp;
}
return kg.compareTo(otherFruit.kg);
}
/* Constructor
* constructs an instance of the Fruit class
* using user defined characteristics
**/
public Fruit(String name, String colour, String mass) {
this.name = name;
col = colour;
mass = kg;
}
}
答案 3 :(得分：0)
如果您的Fruit类实现了java Comparator接口（在google上查找），可以使用Collections.sort来完成。 我试着在你的代码中实现它：
import java.util.*;
/**creates instances of the Fruits class, and stores the
* resulting objects in an array which can be ordered
* firsting alphebetically by name, then by colour, and
* finally, in ascending order by weight
**/
public class Driver
{
public static void main(String[]args)
{
Scanner s = new Scanner(System.in);
int input = 0;
ArrayList fruitInfo = new ArrayList();
do
{
System.out.println("Enter option: (1) add fruit (2) quit (3) to print sorted by name (4) to print sorted by kg:");
input = s.nextInt();
s.nextLine();
switch(input)
{
case 1:{
System.out.println("Enter name, colour and mass in kg separated by a `enter code here`space");
String in = s.nextLine();
String[] temp = in.split(" ");
//create a new instance of the fruit class and add it to the `enter code here`<ArrayList> {@link ArrayList}, fruitInfo
fruitInfo.add(new Fruit(temp[0], temp[1], temp[2]));
break;
}
case 2:{
break;
}
case 3:
Collections.sort(fruitInfo, Fruit.FruitNameComparator);
for(Object fruit:fruitInfo) {
System.out.println(fruit);
}
break;
case 4:
Collections.sort(fruitInfo, Fruit.FruitKgComparator);
for(Object fruit:fruitInfo) {
System.out.println(fruit);
}
break;
default: System.out.println("Input incorrect. Try again.");
}
}
while(input!=2);
}
}
水果班：
import java.util.Comparator;
public class Fruit implements Comparator<Fruit>
{
private String name;
private String col;
private String kg;
/* Constructor
* constructs an instance of the Fruit class
* using user defined characteristics
**/
public Fruit(String name, String colour, String mass)
{
this.name=name;
col=colour;
kg=mass;
}
public static Comparator<Fruit> FruitNameComparator = new Comparator<Fruit>() {
@Override
public int compare(Fruit o1, Fruit o2) {
return o1.name.compareTo(o2.name);
}
};
public static Comparator<Fruit> FruitColComparator = new Comparator<Fruit>() {
@Override
public int compare(Fruit o1, Fruit o2) {
return o1.col.compareTo(o2.col);
}
};
public static Comparator<Fruit> FruitKgComparator = new Comparator<Fruit>() {
@Override
public int compare(Fruit o1, Fruit o2) {
return o1.kg.compareTo(o2.kg);
}
};
@Override
public int compare(Fruit o1, Fruit o2) {
return o1.name.compareTo(o2.name);
}
public String toString() {
return "Name: " + name + " Colour: " + col + " Weight: " +kg;
}
}
这里有一个示例输出：
Enter option: (1) add fruit (2) quit (3) to print sorted by name (4) to print sorted by kg:
1
Enter name, colour and mass in kg separated by a `enter code here`space
a b c
Enter option: (1) add fruit (2) quit (3) to print sorted by name (4) to print sorted by kg:
1
Enter name, colour and mass in kg separated by a `enter code here`space
b c a
Enter option: (1) add fruit (2) quit (3) to print sorted by name (4) to print sorted by kg:
1
Enter name, colour and mass in kg separated by a `enter code here`space
c a b
Enter option: (1) add fruit (2) quit (3) to print sorted by name (4) to print sorted by kg:
3
Name: a Colour: b Weight: c
Name: b Colour: c Weight: a
Name: c Colour: a Weight: b
Enter option: (1) add fruit (2) quit (3) to print sorted by name (4) to print sorted by kg:
4
Name: b Colour: c Weight: a
Name: c Colour: a Weight: b
Name: a Colour: b Weight: c