比较器无法工作

Question

public class Test implements Comparable <Test>{ 
String name; 
int age; 
int salary; 
public Test(String name, int age, int salary){ 
    this.name = name; 
    this.age = age; 
    this.salary = salary; 
} 
public int compareTo(Test newTest){ 
    if (this.name.compareTo(newTest.name) > 0){ 
     return 1; 
    } else if(this.name.compareTo(newTest.name) < 0){ 
     return -1; 
    } else{ 
     return 0; 
    } 
} 

public static void main(String[] args){ 
    Test Albert = new Test("Albert", 19, 100); 
    Test James = new Test("James", 16, 50); 
    if (Albert.compareTo(James) == -1){ 
     System.out.println("Albert Comes first"); 
    } else if (Albert.compareTo(James) == 1){ 
     System.out.println("James Comes first"); 
    } else{ 
     System.out.println("It's a tie"); 
    } 

    int[] testArray = new int[2]; 
    testArray[0] = Albert.age; 
    testArray[1] = James.age; 

    Collections.sort(testArray, new TestComparator()); 
} 
} 

我创建了一个名为TestComparator的比较器，由于某种原因它不适用于Collections.sort。我不知道为什么它不工作。有任何想法吗？我也尝试了Array.sort，它不起作用。任何意见，将不胜感激。

Answer 1

Collections.sort()与List<Integer>一起使用，而不是数组。

Arrays.sort()只适用于int[]如果你想升序。

将阵列更改为Integer[]类型，并且您应该能够使用使用Comparator的版本Arrays.sort()。

Answer 2

以上程序。你只需要使用Arrays.sort（testArray）;

public static void main(String[] args){ 
    Test Albert = new Test("Albert", 19, 100); 
    Test James = new Test("James", 16, 50); 

    if (Albert.compareTo(James) == -1){ 
     System.out.println("Albert Comes first"); 
    } else if (Albert.compareTo(James) == 1){ 
     System.out.println("James Comes first"); 
    } else{ 
     System.out.println("It's a tie"); 
    } 

    int[] testArray = new int[2]; 
    testArray[0] = Albert.age; 
    testArray[1] = James.age; 

    Arrays.sort(testArray); //You are just using int array so no need of Collections.sort 

    for(int temp: testArray){ 
      System.out.println("Age :: " + temp); 
    } 
    //Collections.sort(testArray, new); 
} 
} 

如果你想对对象进行排序，那么你必须使用相当的接口，这将根据您所覆盖compareTo方法内部实现什么样的。

你可以从下面的链接有更好的想法可比较和comparaor。 Java Object Sorting Example (Comparable And Comparator)

Answer 3

看起来你实际想要做的是以不同的方式对Test对象进行排序。

我刚刚得到这个代码用三个例子的工作：使用TestComparator类按年龄排序，排序是由工资内嵌Comparator，并通过默认Comparable进行排序的名字。

下面是使用TestComparator类按年龄排序的示例：

import java.util.Collections; 
import java.util.Comparator; 
import java.util.List; 
import java.util.ArrayList; 

public class Test implements Comparable <Test>{ 
    String name; 
    int age; 
    int salary; 
    public Test(String name, int age, int salary){ 
     this.name = name; 
     this.age = age; 
     this.salary = salary; 
    } 

    @Override 
    public int compareTo(Test newTest){ 
     return (this.name.compareTo(newTest.name)); 
    } 

    public static void main(String[] args){ 

     List<Test> testList = new ArrayList<Test>(); 
     testList.add(new Test("Albert", 19, 100)); 
     testList.add(new Test("James", 16, 50)); 
     testList.add(new Test("Brian", 15, 50)); 

     Collections.sort(testList, new TestComparator()); 

     for (int i = 0; i < testList.size(); i++){ 
     System.out.println(testList.get(i).name); 

     } 
    } 
} 

public class TestComparator implements Comparator<Test>{ 
    @Override 
    public int compare(Test t1, Test t2) { 
    return t1.age-t2.age; 
    } 
} 

这里是由薪金排序直列Comparator：

import java.util.Collections; 
import java.util.Comparator; 
import java.util.List; 
import java.util.ArrayList; 

public class Test implements Comparable <Test>{ 
    String name; 
    int age; 
    int salary; 
    public Test(String name, int age, int salary){ 
     this.name = name; 
     this.age = age; 
     this.salary = salary; 
    } 

    @Override 
    public int compareTo(Test newTest){ 
     return (this.name.compareTo(newTest.name)); 
    } 

    public static void main(String[] args){ 

     List<Test> testList = new ArrayList<Test>(); 
     testList.add(new Test("Albert", 19, 100)); 
     testList.add(new Test("James", 16, 50)); 
     testList.add(new Test("Brian", 15, 60)); 

     Collections.sort(testList, new Comparator<Test>() { 
      @Override 
       public int compare(Test t1, Test t2) { 
        return t1.salary-t2.salary; 
       } 
      }); 

     for (int i = 0; i < testList.size(); i++){ 
     System.out.println(testList.get(i).name); 

     } 
    } 
} 

这里是默认compareTo()方法的例子按名称排序：

import java.util.Collections; 
import java.util.List; 
import java.util.ArrayList; 

public class Test implements Comparable <Test>{ 
    String name; 
    int age; 
    int salary; 
    public Test(String name, int age, int salary){ 
     this.name = name; 
     this.age = age; 
     this.salary = salary; 
    } 

    @Override 
    public int compareTo(Test newTest){ 
     return (this.name.compareTo(newTest.name)); 
    } 

    public static void main(String[] args){ 
     Test Albert = new Test("Albert", 19, 100); 
     Test James = new Test("James", 16, 50); 
     if (Albert.compareTo(James) < 0){ 
      System.out.println("Albert Comes first"); 
     } else if (Albert.compareTo(James) > 0){ 
      System.out.println("James Comes first"); 
     } else{ 
      System.out.println("It's a tie"); 
     } 

     List<Test> testList = new ArrayList<Test>(); 
     testList.add(James); 
     testList.add(Albert); 

     Collections.sort(testList); 

     for (int i = 0; i < testList.size(); i++){ 
     System.out.println(testList.get(i).name); 

     } 
    } 
} 

Answer 4

一行代码

Collections.sort(testArray, new TestComparator()); 

应该抛出编译错误，因为Collections类中没有这样的排序方法。

改为使用Arrays.sort(testArray);它将按升序对数组进行排序。

顺便说一句，你想通过传递一个TestComparator为一组元素做什么？