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Commit e60814b

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1 parent 09f03b1 commit e60814b

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‎Learn/Class_Object_1.java‎

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package Learn;
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public class Class_Object_1
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{
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// 1: Main within the class
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/* In Java, an object is created from a class. We have already created
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the class named Class_Object_1,so now we can use this to create objects.*/
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/* int x=5;
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public static void main(String args[])
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{
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Class_Object_1 myObj = new Class_Object_1();
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System.out.println(myObj.x);
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} */
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// 2: Main outside the class
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/* Java Program to demonstrate having the main method in another
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class Creating Student class. */
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//Creating another class TestStudent1 which contains the main method
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public static void main(String args[])
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{
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Student s1=new Student();
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System.out.println(s1.id);
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System.out.println(s1.name);
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}
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}
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class Student
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{
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int id;
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String name;
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}
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‎Learn/Class_WrapperClasses.java‎

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package Learn;
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/*
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* The wrapper class implements the technique to convert the primitive into object and object into primitive.
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* Primitive data types are faster then Wrapper.
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* There are certain things that only work with Wrapper class e.g. Hibernate, Collection API.
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*/
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public class Class_WrapperClasses
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{
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public static void main(String args[])
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{
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int i = 5; // Primitive data type
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Integer ii = new Integer(5); // Wrapper class
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// Putting a variable inside an object
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Integer ij = new Integer(i); // Boxing - Wrapping
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int j = ij.intValue(); // UnBoxing - UnWrapping
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// Assigning the value to object
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Integer value = i; // AutoBoxing
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int k = value; // AutoUnBoxing
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}
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}

‎Learn/ConstructorOverloading.java‎

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package Learn;
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class ConstructorOverloading
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{
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private int stuID;
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private String stuName;
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private int stuAge;
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ConstructorOverloading()
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{
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stuID = 100;
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stuName = "New Student";
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stuAge = 17;
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}
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ConstructorOverloading(int num1, String str, int num2)
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{
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stuID = num1;
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stuName = str;
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stuAge = num2;
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}
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/* The get method returns the variable value, and the set method sets the value.
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However, as the name variable is declared as private, we cannot access it from outside this class. */
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//Getter and setter methods
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public int getStuID()
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{
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return stuID;
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}
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public void setStuID(int stuID)
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{
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this.stuID = stuID;
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}
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public String getStuName()
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{
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return stuName;
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}
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public void setStuName(String stuName)
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{
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this.stuName = stuName;
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}
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public int getStuAge()
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{
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return stuAge;
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}
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public void setStuAge(int stuAge)
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{
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this.stuAge = stuAge;
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}
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public static void main(String args[])
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{
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ConstructorOverloading obj = new ConstructorOverloading();
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System.out.println("Student Name is: "+obj.getStuName());
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System.out.println("Student Age is: "+obj.getStuAge());
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System.out.println("Student ID is: "+obj.getStuID());
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ConstructorOverloading obj2 = new ConstructorOverloading(555, "Chat", 25);
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System.out.println("Student Name is: "+obj2.getStuName());
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System.out.println("Student Age is: "+obj2.getStuAge());
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System.out.println("Student ID is: "+obj2.getStuID());
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}
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}
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‎Learn/CopyConstructor.java‎

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package Learn;
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class JavaExample
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{
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String web;
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JavaExample(String a)
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{
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web = a;
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}
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// It copies the values of one object to the another object (the object that invokes this constructor)
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JavaExample(JavaExample ref)
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{
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web = ref.web;
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}
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void disp()
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{
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System.out.println("Website: "+web);
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}
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}
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public class CopyConstructor
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{
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public static void main(String args[])
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{
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JavaExample obj1 = new JavaExample("BeginnersBook");
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// Passing the object as an argument to the constructor. This will invoke the copy constructor
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JavaExample obj2 = new JavaExample(obj1);
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obj1.disp();
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obj2.disp();
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}
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}

‎Learn/DataInputStream_class.java‎

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package Learn;
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import java.io.*;
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public class DataInputStream_class
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{
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public static void main(String args[])throws IOException
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{
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DataInputStream in = new DataInputStream(System.in);
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/*System.out.println("Enter Your Name: ");
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String name =in.readLine();
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System.out.println("Name: "+name);
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System.out.println("Enter Your Age: ");
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int age =Integer.parseInt(in.readLine());
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System.out.println("Age: "+age);*/
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System.out.println("Enter Character: ");
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char c=(char)System.in.read();
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System.out.println("Gender: "+c);
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// float = Float.parseFloat(in.readLine()); & double = Double.parseDouble(in.readLine());
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}
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}

‎Learn/Enum.java‎

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package Learn;
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/* Enum is short of this
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class Mobile
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{
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static final Mobile APPLE = new Mobile(100);
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static final Mobile SAMSUNG = new Mobile();
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static final Mobile HTC = new Mobile(90);
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}*/
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interface demo3
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{ } // enum can implement but can't extend
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enum Mobile implements demo3
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{
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// Two ways we can set price:
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// direct method for apple and htc
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APPLE(100), SAMSUNG, HTC(90);
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// using constructor & methods for samsung
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int price;
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Mobile()
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{
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price = 80;
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}
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Mobile(int p)
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{
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price = p;
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}
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public int getPrice()
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{
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return price;
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}
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}
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public class Enum
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{
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public static void main(String args[])
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{
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System.out.println(Mobile.APPLE.getPrice());
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System.out.println(Mobile.SAMSUNG.getPrice());
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System.out.println(Mobile.HTC.getPrice());
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Mobile m[] = Mobile.values();
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for(Mobile mobile : m)
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System.out.println(mobile);
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}
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}

‎Learn/EqualsMethod.java‎

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package Learn;
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/* .equals()
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* In general, both equals() and "==" operators in Java are used to compare objects to check equality, but here are some of the differences between the two:
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* The main difference between the .equals() method and == operator is that one is a method, and the other is the operator.
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* We can use == operators for reference comparison (address comparison) and .equals() method for content comparison. In simple words, == checks if both objects point to the same memory location whereas .equals() evaluates to the comparison of values in the objects.
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* If a class does not override the equals method, then by default, it uses the equals(Object o) method of the closest parent class that has overridden this method.
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*/
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public class EqualsMethod
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{
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public static void main(String args[])
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{
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String s1 = "HELLO";
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String s2 = "HELLO";
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String s3 = new String("HELLO");
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System.out.println(s1 == s2); // true
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System.out.println(s1 == s3); // false
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System.out.println(s1.equals(s2)); // true
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System.out.println(s1.equals(s3)); // true
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}
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}
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/* Explanation: Here, we create two objects, namely s1 and s2.
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* Both s1 and s2 refer to different objects.
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* When we use the == operator for s1 and s2 comparison, the result is true as both have the same addresses in the string constant pool.
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* Using equals, the result is true because it’s only comparing the values given in s1 and s2. */

‎Learn/GUIApplets.java‎

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package Learn;
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import java.applet.*;
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import java.awt.*;
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/* <applet CODE="GUIApplets.class" WIDTH=400 HEIGHT=600>
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</applet> */
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public class GUIApplets extends Applet
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{
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public void init()
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{
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setBackground(Color.black);
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setForeground(Color.white);
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}
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public void paint(Graphics g)
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{
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// Classes:
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Color c = new Color(0,255,0);
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Font f = new Font("Bookman Old Style",3,30);
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g.setColor(c);
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g.setFont(f);
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// Methods:
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int x[] = {200, 250, 260, 270, 290};
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int y[] = {100, 200, 300, 400, 500};
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g.drawPolygon(x,y,5);
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g.drawString("Welcome to Applets",40,40);
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g.drawLine(40,240,100,40);
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g.drawRect(40, 70, 100, 100);
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g.drawRect(20, 20, 100, 100); // its a SQUARE
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g.fillRect(40, 70, 100, 100);
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g.drawOval(40, 170, 30, 30);
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g.drawOval(40, 40, 30, 30); // its a CIRCLE
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g.fillOval(40, 170, 30, 30);
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g.drawArc(40,260,60,100,60,60);
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}
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}

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