compare()方法如何在Java

先决条件：比较接口在Java中，TreeSet中使用Java

Java的compare()方法比较作为参数给出的两个特定于类的对象(x，y)。它返回值：

• 0：如果(x == y)
• -1：如果(x
• 1：如果(x> y)

句法：

public int compare(Object obj1, Object obj2)

其中obj1和obj2是使用compare()方法进行比较的两个对象。

例子：

展示使用Integer类的compare()方法的工作方式。

// Java program to demonstrate working
// of compare() method using Integer Class
  
import java.lang.Integer;
  
class Gfg {
  
    // driver code
    public static void main(String args[])
    {
        int a = 10;
        int b = 20;
  
        // as 10 less than 20,
        // Output will be a value less than zero
        System.out.println(Integer.compare(a, b));
  
        int x = 30;
        int y = 30;
  
        // as 30 equals 30,
        // Output will be zero
        System.out.println(Integer.compare(x, y));
  
        int w = 15;
        int z = 8;
  
        // as 15 is greater than 8,
        // Output will be a value greater than zero
        System.out.println(Integer.compare(w, z));
    }
}

输出：

-1
0
1

如何评估返回值：

compare()方法的内部工作可以在以下伪代码的帮助下可视化：

// Converting the two objects to integer
// for comparison
int intObj1 = (int)obj1;
int intObj2 = (int)obj2;
  
// Get the difference
int difference = intObj1 - intObj2;
  
if (difference == 0) {
  
    // Both are equal
    return 0;
}
else if (difference < 0) {
  
    // obj1 < obj2
    return -1;
}
else {
  
    // obj1 > obj2
    return 1;
}

用这种方法可视化compare()方法：

// Java program to demonstrate working
// of compare() method
  
import java.lang.Integer;
  
class Gfg {
  
    // Function to compare both objects
    public static int compare(Object obj1, Object obj2)
    {
  
        // Converting the two objects to integer
        // for comparison
        int intObj1 = (int)obj1;
        int intObj2 = (int)obj2;
  
        // Get the difference
        int difference = intObj1 - intObj2;
  
        if (difference == 0) {
  
            // Both are equal
            return 0;
        }
        else if (difference < 0) {
  
            // obj1 < obj2
            return -1;
        }
        else {
  
            // obj1 > obj2
            return 1;
        }
    }
  
    // driver code
    public static void main(String args[])
    {
        int a = 10;
        int b = 20;
  
        // as 10 less than 20,
        // Output will be a value less than zero
        System.out.println(compare(a, b));
  
        int x = 30;
        int y = 30;
  
        // as 30 equals 30,
        // Output will be zero
        System.out.println(compare(x, y));
  
        int w = 15;
        int z = 8;
  
        // as 15 is greater than 8,
        // Output will be a value greater than zero
        System.out.println(compare(w, z));
    }
}

输出：

-1
0
1

compare()方法的各种可能实现

public int compare(Object obj1, Object obj2)
{
    Integer I1 = (Integer)obj1; // typecasting object type into integer type
    Integer I2 = (Integer)obj2; // same as above ..
    // 1.
    return I1.compareTo(I2); // ascending order [0, 5, 10, 15, 20]
    // 2.
    return -I1.compareTo(I2); // descending order [20, 15, 10, 5, 0]
    // 3.
    return I2.compareTo(I1); // descending order [20, 15, 10, 5, 0]
    // 4.
    return -I2.compareTo(I1); // ascending order [0, 5, 10, 15, 20]
    // 5.
    return +1; // insertion order [10, 0, 15, 5, 20, 20]
    // 6.
    return -1; // reverse of insertion order [20, 20, 5, 15, 0, 10]
    // 7.
    return 0; // only first element [10]
}