Java Class 3

February 20^th, 2021

Table of Contents

• Class recording
• Resources
• Class content

Class Recording

Combined Panel

Resources

• Learning Resources: Link to all books and online learning resoruces for Java.
• Softablitz 2k20 Classes: Softablitz is the software development event which targets building solutions for problem statements using Java.
• Git Basics Book: Book to cover git basics. Getting well versed with git and github is important, you will use git in all your projects.

Explore as much as you can, go through all the recordings and resources. Wishing you all the best!!

Class Content

12.java

// Demonstrating some String methods.
class StringDemo2 {
    public static void main(String args[]) {
        String strOb1 = "First String";
        String strOb2 = "Second String";
        String strOb3 = strOb1;

        System.out.println("Length of strOb1: " + strOb1.length());

        System.out.println("Char at index 3 in strOb1: " + strOb1.charAt(3));

        if (strOb1.equals(strOb2))
            System.out.println("strOb1 == strOb2");
        else
            System.out.println("strOb1 != strOb2");

        if (strOb1.equals(strOb3))
            System.out.println("strOb1 == strOb3");
        else
            System.out.println("strOb1 != strOb3");
    }
}

13.java

// Demonstrate method overloading.
class OverloadDemo {
    void test() {
        System.out.println("No parameters");
    }

    // Overload test for one integer parameter.
    void test(int a) {
        System.out.println("a: " + a);
    }

    // Overload test for two integer parameters.
    void test(int a, int b) {
        System.out.println("a and b: " + a + " " + b);
    }

    // overload test for a double parameter
    double test(double a) {
        System.out.println("double a: " + a);
        return a * a;
    }
}

class Overload {
    public static void main(String args[]) {
        OverloadDemo ob = new OverloadDemo();
        double result;

        // call all versions of test()
        ob.test();
        ob.test(10);
        ob.test(10, 20);
        result = ob.test(123.25);
        System.out.println("Result of ob.test(123.25): " + result);
    }
}

14.java

// Automatic type conversions apply to overloading.
class OverloadDemo {
    void test() {
        System.out.println("No parameters");
    }

    // Overload test for two integer parameters.
    void test(int a, int b) {
        System.out.println("a and b: " + a + " " + b);
    }

    // overload test for a double parameter and return type
    void test(double a) {
        System.out.println("Inside test(double) a: " + a);
    }
}

class Overload {
    public static void main(String args[]) {
        OverloadDemo ob = new OverloadDemo();
        int i = 88;

        ob.test();
        ob.test(10, 20);

        ob.test(i); // this will invoke test(double)
        ob.test(123.2); // this will invoke test(double)
    }
}

15.java

/* Here, Box defines three constructors to initialize
   the dimensions of a box various ways.
*/
class Box {
    double width;
    double height;
    double depth;
  
    // constructor used when all dimensions specified
    Box(double w, double h, double d) {
      width = w;
      height = h;
      depth = d;
    }
  
    // constructor used when no dimensions specified
    Box() {
      width = -1;  // use -1 to indicate
      height = -1; // an uninitialized
      depth = -1;  // box
    }
  
    // constructor used when cube is created
    Box(double len) {
      width = height = depth = len;
    }
  
    // compute and return volume
    double volume() {
      return width * height * depth;
    }
  }
    
  class OverloadCons {
    public static void main(String args[]) {
      // create boxes using the various constructors
      Box mybox1;
      mybox1 = new Box(10, 20, 15);
      Box mybox2 = new Box();
      Box mycube = new Box(7);
  
      double vol;
  
      // get volume of first box
      vol = mybox1.volume();
      System.out.println("Volume of mybox1 is " + vol);
  
      // get volume of second box
      vol = mybox2.volume();
      System.out.println("Volume of mybox2 is " + vol);
  
      // get volume of cube
      vol = mycube.volume();
      System.out.println("Volume of mycube is " + vol);
    }
  }

16.java

// Objects may be passed to methods.
class Test {
    int a, b;

    Test(int i, int j) {
        a = i;
        b = j;
    }

    // return true if o is equal to the invoking object
    boolean equalTo(Test o) {
        if (o.a == a && o.b == b)
            return true;
        else
            return false;
    }
}

class PassOb {
    public static void main(String args[]) {
        Test ob1 = new Test(100, 22);
        Test ob2 = new Test(100, 22);
        Test ob3 = new Test(-1, -1);

        System.out.println("ob1 == ob2: " + ob1.equalTo(ob2));

        System.out.println("ob1 == ob3: " + ob1.equalTo(ob3));
    }
}

17.java

// Simple Types are passed by value.
class Test {
    void meth(int i, int j) {
        i *= 2;
        j /= 2;
    }
}

class CallByValue {
    public static void main(String args[]) {
        Test ob = new Test();
        int a = 15, b = 20;

        System.out.println("a and b before call: " + a + " " + b);

        ob.meth(a, b);

        System.out.println("a and b after call: " + a + " " + b);
    }
}

18.java

// Objects are passed through their references.

class Test {
    int a, b;

    Test(int i, int j) {
        a = i;
        b = j;
    }

    // pass an object
    void meth(Test o) {
        o.a *= 2;
        o.b /= 2;
    }
}

class PassObjRef {
    public static void main(String args[]) {
        Test ob = new Test(15, 20);

        System.out.println("ob.a and ob.b before call: " + ob.a + " " + ob.b);

        ob.meth(ob);

        System.out.println("ob.a and ob.b after call: " + ob.a + " " + ob.b);
    }
}

We encourage you to run the shared code and feel free to experiment with it. In case of any doubt just ping any of the co-ordinators we are always here to help :)