Java Object数组数值比较报错：如何实现大于/小于判断？

Let's break down the issues in your code and fix them step by step:

First, two critical mistakes are causing your error:

• Wrong array index: You're trying to compare Person[i][0] (which stores the person's name, a String) to the number 18. Strings and integers can't be compared directly—you meant to use Person[i][1], which holds the age as an Integer object.
• Object type limitation: Your array is of type Object[][], so elements are treated as generic Objects. These don't support numerical comparison operators like < or >. You need to cast the Object back to an Integer (or int) first to perform the check.

Solution 1: Cast the Object to Integer for Direct Comparison #

You can safely cast the age element to an int (or Integer) to run the numerical comparison. Here's the corrected version of your original code:

Object[][] Person = new Object[2][2];
Person[0][0] = "John";
Person[0][1] = new Integer(18);

Person[1][0] = "Mike";
Person[1][1] = new Integer(42);


for(int i = 0; i < Person.length; i++)
{
    System.out.print(Person[i][0]);
    System.out.print("\t" + Person[i][1] + "\t");

    // Cast the Object to int first, then compare
    int age = (int) Person[i][1];
    if(age < 18)
    {
        System.out.print("Under 18");
    } else {
        System.out.print("18 or over");
    }    

    System.out.println();
}  

If you prefer working with the Integer object directly, you can use its compareTo() method:

Integer age = (Integer) Person[i][1];
if(age.compareTo(18) < 0) {
    System.out.print("Under 18");
} else {
    System.out.print("18 or over");
}

Solution 2: Use a Custom Person Class (Cleaner, Type-Safe Approach) #

For more maintainable and error-free code, it's better to create a dedicated Person class instead of relying on an Object[][] array. This eliminates casting entirely and makes your code more readable:

class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() { return name; }
    public int getAge() { return age; }
}

public class Main {
    public static void main(String[] args) {
        Person[] people = new Person[2];
        people[0] = new Person("John", 18);
        people[1] = new Person("Mike", 42);

        for(Person person : people) {
            System.out.print(person.getName());
            System.out.print("\t" + person.getAge() + "\t");

            if(person.getAge() < 18) {
                System.out.print("Under 18");
            } else {
                System.out.print("18 or over");
            }

            System.out.println();
        }
    }
}

This approach is far more scalable if you ever need to add more attributes to your Person objects later.

内容的提问来源于stack exchange，提问作者Bradie