All Flashcards
What are the key differences between private and public access modifiers?
Private: accessible only within the class. Public: accessible from any class.
Compare local and global variables in terms of scope.
Local: limited to the block they are defined in. Global: accessible throughout the class.
What are the differences between 'package' and 'protected' access modifiers?
Package: accessible within the same package. Protected: accessible within the same package and by subclasses in other packages.
Contrast the use cases of public instance variables vs. private instance variables with public getter/setter methods.
Public instance variables: simpler but violate encapsulation. Private with getters/setters: more complex but allows controlled access and modification.
Compare the scope of static vs. instance variables.
Static: class-level scope, shared by all instances. Instance: object-level scope, unique to each instance.
Differentiate between access modifiers and scope.
Access modifiers: control visibility from outside the class. Scope: determines where a variable is accessible within the code.
Compare the accessibility of a variable declared without any access modifier versus one declared as public.
No modifier (package-private): accessible only within the same package. public: accessible from anywhere.
Contrast the impact of using private vs. protected members in the context of inheritance.
private: not accessible to subclasses. protected: accessible to subclasses, allowing for controlled inheritance.
Compare the use of local variables inside a method versus parameters passed to the method.
Local variables: declared and initialized within the method. Parameters: passed into the method from the caller.
Contrast the scope of a variable declared inside an 'if' statement block versus a variable declared outside the 'if' statement but within the same method.
Inside 'if': scope limited to the 'if' block. Outside 'if': scope extends to the entire method (excluding shadowed regions).
What is the scope of 'x' in: public void method() { int x = 5; }?
Local scope; only accessible within the method() method.
Given: private int age; can another class directly access age?
No, age is private and only accessible within its own class.
java
public class Test {
private int x = 10;
public void printX() {
System.out.println(x);
}
}
public class Main {
public static void main(String[] args) {
Test t = new Test();
System.out.println(t.x); // What happens here?
}
}
Compile-time error: x is private and cannot be accessed from Main.
java
public class A {
int x = 5; // package access
}
public class B {
public static void main(String[] args) {
A a = new A();
System.out.println(a.x); // When is this valid?
}
}
Valid only if A and B are in the same package.
java
public class Parent {
protected int value = 10;
}
public class Child extends Parent {
public void printValue() {
System.out.println(value);
}
}
Is value accessible in Child?
Yes, value is protected and accessible in subclasses.
java
public class Example {
public int x;
public Example(int x) {
this.x = x;
}
public static void main(String[] args) {
Example e = new Example(5);
System.out.println(e.x); // What is the output?
}
}
5
java
public class Test {
private static int count = 0;
public Test() {
count++;
}
public static int getCount() {
return count;
}
public static void main(String[] args) {
Test t1 = new Test();
Test t2 = new Test();
System.out.println(Test.getCount()); // What is the output?
}
}
2
java
public class ScopeTest {
int x = 10;
public void methodA() {
int x = 20;
System.out.println(x); // What is the output?
}
public static void main(String[] args) {
ScopeTest st = new ScopeTest();
st.methodA();
}
}
20
java
public class AccessTest {
private int secret = 5;
public int getSecret() {
return secret;
}
public static void main(String[] args) {
AccessTest at = new AccessTest();
System.out.println(at.secret); // Will this compile?
}
}
No, it will not compile. secret is private and cannot be accessed directly from main.
java
public class Test {
public static void main(String[] args) {
int x = 5;
if (true) {
int x = 10; // Is this allowed?
System.out.println(x);
}
System.out.println(x);
}
}
Yes, it's allowed. The inner x shadows the outer x within the if block. Output: 10, 5
What is the significance of local scope?
It limits variable access, preventing unintended modifications and promoting modularity.
What is the significance of global scope?
It allows variables to be accessed from anywhere in the class, but can increase the risk of unintended side effects.
Why are instance variables often declared private?
To encapsulate data and control access to the object's state.
What is the purpose of access modifiers in object-oriented programming?
To control the visibility and accessibility of class members, enforcing encapsulation and abstraction.
Explain the concept of data hiding.
Restricting access to the internal representation of an object, preventing direct manipulation from outside the class.
What happens when a local variable has the same name as a global variable?
The local variable takes precedence within its scope, shadowing the global variable.
How does inheritance relate to the 'protected' access modifier?
Protected members are accessible by subclasses, enabling inheritance while still providing some level of encapsulation.
What is the role of the 'public' access modifier in class design?
It defines the interface of the class, specifying which methods and constructors are accessible from other classes.
Why is understanding scope important for debugging?
Knowing the scope of variables helps identify where a variable's value might be unexpectedly changed or accessed.
How do static variables relate to scope and access?
Static variables have class-level scope and are shared by all instances of the class. Their access is controlled by access modifiers.