Scope

public class Student {
    private String name;     // accessible in ALL methods below
    private double gpa;
    
    public Student(String name, double gpa) {
        this.name = name;    // can access name here
        this.gpa = gpa;
    }
    
    public String getName() {
        return name;         // can access name here
    }
    
    public boolean isHonors() {
        return gpa >= 3.5;   // can access gpa here
    }
}

public class Example {
    public void method1() {
        int x = 10;          // x exists only in method1
        System.out.println(x);
    }
    
    public void method2() {
        // System.out.println(x);  // COMPILE ERROR — x doesn't exist here
        int y = 20;          // y exists only in method2
    }
}

public void setAge(int age) {
    this.age = age;   // parameter age exists here
}

public void printInfo() {
    // System.out.println(age);  // This refers to instance variable, not the parameter!
}

public void demo() {
    // Loop variable — only exists inside the loop
    for (int i = 0; i < 10; i++) {
        int doubled = i * 2;   // only exists inside loop body
        System.out.println(doubled);
    }
    // i is gone here
    // doubled is gone here
    
    // If block variable
    if (true) {
        int temp = 42;
        System.out.println(temp);   // works
    }
    // temp is gone here
}

public class Point {
    private int x = 10;
    
    public void setX(int x) {
        // x here refers to the PARAMETER, not the instance variable
        System.out.println(x);        // parameter
        System.out.println(this.x);   // instance variable
        this.x = x;                   // set instance var to parameter
    }
}

Point p = new Point();
p.setX(5);
// prints: 5 (parameter)
//         10 (instance variable, before assignment)

public class Student {
    private String name;
    private static int count = 0;   // shared by ALL Student objects
    
    public Student(String name) {
        this.name = name;
        count++;   // increment every time a new Student is created
    }
    
    // Static method — belongs to the class
    public static int getCount() {
        return count;
    }
    
    // Instance method — belongs to an object
    public String getName() {
        return name;
    }
}

System.out.println(Student.getCount());  // 0
Student s1 = new Student("Alice");       // count = 1
Student s2 = new Student("Bob");         // count = 2
System.out.println(Student.getCount());  // 2

// Static method CANNOT access instance variables:
public static int getCount() {
    // return name;   // COMPILE ERROR — name is instance variable
    return count;     // works — count is static
}

// Instance method CAN access both:
public String getInfo() {
    return name + " (#" + count + ")";  // both work
}

public class ScopeDemo {
    private int x = 1;
    
    public int method(int x) {
        // Parameter x shadows instance variable x
        int y = x + this.x;   // parameter + instance var
        for (int i = 0; i < 3; i++) {
            y += i;
        }
        return y;
    }
}

ScopeDemo demo = new ScopeDemo();
int result = demo.method(5);