import java.util.Arrays;
/**
* generic_swap
* ------------
* A fully generic Java swap function implemented using generics.
*
* Parameters:
* a, b - wrapper objects whose internal values will be swapped
*
* Java does not allow swapping primitives directly because they are
* passed by value. To emulate C++ reference semantics, we wrap primitive
* values in small mutable classes (IntBox, DoubleBox).
*
* This function works for:
* - boxed primitive wrappers (IntBox, DoubleBox)
* - Strings (reference swap)
* - user‑defined classes
*/
class Swap {
public static <T> void genericSwap(Box<T> a, Box<T> b) {
T temp = a.value;
a.value = b.value;
b.value = temp;
}
}
/**
* Simple generic wrapper class to simulate pass‑by‑reference.
*/
class Box<T> {
public T value;
public Box(T value) { this.value = value; }
}
/**
* Mutable wrappers for primitive types
*/
class IntBox extends Box<Integer> {
public IntBox(int v) { super(v); }
}
class DoubleBox extends Box<Double> {
public DoubleBox(double v) { super(v); }
}
/**
* Java equivalent of the C++ struct Point
*/
class Point {
public int x, y;
public Point(int x, int y) { this.x = x; this.y = y; }
@Override
public String toString() {
return "(" + x + "," + y + ")";
}
}
/**
* Print arrays of integers
*/
class Utils {
public static void printIntArray(int[] arr) {
for (int v : arr)
System.out.print(v + " ");
System.out.println();
}
}
public class Main {
public static void main(String[] args) {
System.out.println("=== TEST 1: Swap integers ===");
IntBox x = new IntBox(10);
IntBox y = new IntBox(20);
System.out.println("Before: x=" + x.value + ", y=" + y.value);
Swap.genericSwap(x, y);
System.out.println("After: x=" + x.value + ", y=" + y.value + "\n");
System.out.println("=== TEST 2: Swap doubles ===");
DoubleBox a = new DoubleBox(3.14);
DoubleBox b = new DoubleBox(2.71);
System.out.println("Before: a=" + a.value + ", b=" + b.value);
Swap.genericSwap(a, b);
System.out.println("After: a=" + a.value + ", b=" + b.value + "\n");
System.out.println("=== TEST 3: Swap structs ===");
Point p1 = new Point(1, 2);
Point p2 = new Point(9, 8);
System.out.println("Before: p1=" + p1 + ", p2=" + p2);
Box<Point> bp1 = new Box<>(p1);
Box<Point> bp2 = new Box<>(p2);
Swap.genericSwap(bp1, bp2);
System.out.println("After: p1=" + bp1.value + ", p2=" + bp2.value + "\n");
System.out.println("=== TEST 4: Swap array elements ===");
int[] arr = {1, 2, 3, 4, 5};
System.out.print("Before: ");
Utils.printIntArray(arr);
int temp = arr[1];
arr[1] = arr[3];
arr[3] = temp;
System.out.print("After: ");
Utils.printIntArray(arr);
System.out.println();
System.out.println("=== TEST 5: Swap strings ===");
Box<String> str1 = new Box<>("Hello");
Box<String> str2 = new Box<>("World");
System.out.println("Before: str1=\"" + str1.value + "\", str2=\"" + str2.value + "\"");
Swap.genericSwap(str1, str2);
System.out.println("After: str1=\"" + str1.value + "\", str2=\"" + str2.value + "\"\n");
}
}
/*
run:
=== TEST 1: Swap integers ===
Before: x=10, y=20
After: x=20, y=10
=== TEST 2: Swap doubles ===
Before: a=3.14, b=2.71
After: a=2.71, b=3.14
=== TEST 3: Swap structs ===
Before: p1=(1,2), p2=(9,8)
After: p1=(9,8), p2=(1,2)
=== TEST 4: Swap array elements ===
Before: 1 2 3 4 5
After: 1 4 3 2 5
=== TEST 5: Swap strings ===
Before: str1="Hello", str2="World"
After: str1="World", str2="Hello"
*/
