Prerequisite: Comparator Interface in Java, TreeSet in Java
The compare() method in Java compares two class specific objects (x, y) given as parameters. It returns the value:
- 0: if (x==y)
- -1: if (x < y)
- 1: if (x > y)
Syntax:
public int compare(Object obj1, Object obj2)
where obj1 and obj2 are the two objects to be compared using compare() method.
Example:
To show working of compare() method using Integer Class.
Java
// Java program to demonstrate working// of compare() method using Integer Classimport 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)); }} |
Output:
-1 0 1
How is the return value evaluated:
The internal working of the compare() method can be visualized with the help of below pseudocode:
Java
// Converting the two objects to integer// for comparisonint intObj1 = (int)obj1;int intObj2 = (int)obj2;// Get the differenceint difference = intObj1 - intObj2;if (difference == 0) { // Both are equal return 0;}else if (difference < 0) { // obj1 < obj2 return -1;}else { // obj1 > obj2 return 1;} |
Visualizing the compare() method with this approach:
Java
// Java program to demonstrate working// of compare() methodimport 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)); }} |
Output:
-1 0 1
Various possible implementations of compare() method
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]
}
