جافا Java

❓ equals مقابل == مع السلاسل equals vs == with Strings

String s1 = new String("java");
String s2 = new String("java");
System.out.println(s1.equals(s2) + "," + (s1 == s2));

❓ instanceof مع الوراثة instanceof with inheritance

class A {}
class B extends A {}
A x = new A();
System.out.println(x instanceof B);

❓ تعدد الأشكال (Polymorphism) Polymorphism dispatch

class A { String f(){ return "A"; } }
class B extends A { String f(){ return "B"; } }
A x = new B();
System.out.println(x.f());

❓ استخدام super في override Using super in an override

class A { String f(){ return "A"; } }
class B extends A { String f(){ return super.f() + "B"; } }
System.out.println(new B().f());

❓ سَلسَلة المُنشئات باستخدام this Constructor chaining with this

class P {
  int x; 
  P(){ this(5); }
  P(int x){ this.x = x; }
}
System.out.println(new P().x);

❓ ما أقل معدِّل وصول يسمح لوريث في حزمة مختلفة؟ What is the least permissive modifier that still allows a subclass in a different package to access a member?

❓ ما ناتج التعامل مع static مقابل instance؟ What prints for static vs instance fields?

class C { static int s=0; int i=0; C(){ s++; i++; } }
C a = new C();
C b = new C();
System.out.println(C.s + "," + b.i);

❓ أي عبارة صحيحة عن Overloading/Overriding؟ Which statement is true about overloading/overriding?

❓ ما قيمة الحقل بعد إنشاء الكائن؟ What is the field value after object creation?

class A { int v = 1; A(){ v *= 2; } }
A a = new A();
System.out.println(a.v);

❓ ما مجموع التأثير في switch مع default؟ Total effect in switch with default?

int x = 0;
int v = 3;
switch (v) {
  case 1: x += 1; break;
  case 2:
  case 3: x += 3;
  default: x += 5; break;
}
System.out.println(x);