// INHERIT17_equals

// Another handy feature of $Object$ is the $equals$ method.

// In general, if you use $==$ to compare to objects for equality, you
// will just be testing if to objects have the same address. The
// equality relation $==$ does NOT test for equality of objects'
// CONTENTS.

// To test equality of contents, use the $equals$ method inherited
// from $Object$. Note that unless you override $equals$, Java
// typically gives you $==$!

public class inherit17_equals {
    public static void main(String[] args) {

	A a1 = new A(1);
	A a2 = new A(2);
	A a3 = new A(2);

	// Test if $a1$ and $a2$ refer to same object: You will see
	// `no' because the references point to different objects.
	if (a1 == a2) System.out.println("Test 1: yes");
	else  System.out.println("Test 1: no");
	
	// Test if $a1$ and $a2$ have the same contents: You will see
	// `no' because the references still point to different objects:
	if (a1.equals(a2)) System.out.println("Test 2: yes");
	else  System.out.println("Test 2: no");
	
	// Test if $a2$ and $a3$ have the same contents: Yes, you
	// STILL see `no' because Java uses the default meaning $==$:
	if (a3.equals(a2)) System.out.println("Test 3: yes");
	else  System.out.println("Test 3: no");

	// To use $equals$ to test contents, investigate the
	// implementation in Class B. You will see `yes' this time
	// because the objects have equal contents as defined by the $equals$
	// method that's written in Class B:
	B b1 = new B(1);
	B b2 = new B(1);
	if (b1.equals(b2)) System.out.println("Test 4: yes");
	else  System.out.println("Test 4: no");

	// Strings have $equals$ defined as equality of contents,
	// so you will get `yes' again:
	String s1 = new String("hi");
	String s2 = new String("hi");
	if (s1.equals(s2)) System.out.println("Test 5: yes");
	else  System.out.println("Test 5: no");

	// Arrays do NOT have $equals$ defined as equality of contents:
	int[] x1 = {1,2,3};
	int[] x2 = {1,2,3};
	if (x1.equals(x2)) System.out.println("Test 6: yes");
	else  System.out.println("Test 6: no");
	// But, there is an $equals$ defined for arrays in java.util.arrays!
    }
}

class A {
    public int k;
    public A(int k) { this.k = k; }
}

class B extends A{
    public B(int k) { super(k); }

    public boolean equals(B b) {
	if (k==b.k) return true;
	return false;
    }
}

/* Output:
Test 1: no
Test 2: no
Test 3: no
Test 4: yes
Test 5: yes
Test 6: no
*/