Core Java(Part-5)

Content

1.Methods

.Predefined methods

.Userdefined methods

.Method without parameter without return type

.Method with parameter without return type

.Method without parameter with return type

.Method with parameter with return type

2.String

Methods

Types in Method

predefined method

eg:- System.out.println(), Math.sqrt(), etc.

User defined methods

eg:- sayHello(), addNumbers()

In java methods is of 4 types

1. Method without parameter without return type

use when you didn’t return anything

Syntax:-

public void hello(){

    int a=12;

    System.out.println(a);

}

2. Method with return type without parameter

Syntax:-

public int hello1(){

    int a=12;

    int b=10;

    int c=a+b;

    return c;

}

3. Method without return type with parameter

Syntax:-

public class MethodWithParameterWithoutReturnType  {
    public static void main(String args[]){
        hello1(10);
    }
    public static void hello1(int a) {

        int a1 = a;

        System.out.println(a1);

    }
}

4. Method with parameter with return type

Syntax:-

public class MethodWithParameterWithReturnType {
    public static void main(String args[]){
       System.out.println(hello1(10,20));
    }
    public static int hello1(int a, int b) {

        int a1 = a;
        int b1=b;

        return a1+b1;

    }
}

In lame term

Instead of cooking every time from scratch, you press a button on your sandwich maker 🥪 That button is like a method — it does a specific job when you call it.

void makeSandwich() {

    System.out.println("Bread + Sauce + Cheese = Sandwich ");

}

Now wherever you say

makeSandwich();

Java be like:

“On it, boss! Sandwich aa gaya”

String

String in simple words sentence, words, letter of collection.

In java when you have to handle something like someone name, message or sentence there we use String.

String name=”Khelendra”;

System.out.println(name);

String text enclosed in double quotes(““)

String is a class in java, but to use String is very easy like using other datatype (int, float) etc.

String are immutable means when you create String variable and store value in it after initialization you cannot reinitialized it(you can’t change the value again)

Common String function

1. length()

It tells how many character in String

String str=”Khelendra”

System.out.println(str.length());//9

2.toUpperCase() / toLowerCase()

toUpperCase() It convert the String into capital letter(upper case)

toLowerCase() It convert the String into small letter(lower case)

str.toUpperCase(); // "KHELENDRA"

str.toLowerCase(); // "khelendra"

3.charAt(index)

It tells in which position which letter are at

str.charAt(2);//

4.equals() vs ==

equals() it check actual content inside the variable

== it check memory allocation(reference address)

public class StringComparision{

    public static void main(String args[]){

        String s1="Hello";

        String s2="Hello";

        System.out.println(s1==s2);//true

        System.out.println(s1.equals(s2));//true

                String s3=new String("Hello");

                System.out.println(s1==s3);//false

        System.out.println(s1.equals(s3));//true

    }

}

Whenever you use new keyword then it create two object first object is create in heap and second object is create in string constant pool(scp)

Whenever you create String then it goes to two area first in heap or second in String constant pool

String Constant Pool(SCP)

. Java create a special place for String in SCP

. When you try to create a one more same String then java didn’t create a new duplicate String of that old String in place of that it gives you the old one

. It saves the memory

Heap

When you use new String() then java forcefully create new object whether in it the data is same.

StringBuffer

It is mutable, also thread safe

public class StringBufferDemo{

    public static void main(String args[]){

        StringBuffer sb=new StringBuffer(“Khelendra“);

        sb.append(“Thakur“);

        System.out.println(sb);

    }

}

String and StringBuffer

public class StringAndStringBuffer{

    public static void main(String args[]){

        String s1=”hello”;

        String s2=s1.concat(“world“);

        System.out.println(s1);//hello

        System.out.println(s2);//helloworld (new object created)

        StringBuffer sb=new StringBuffer(“raj“);

        StringBuffer sb1=sb.append(“yadav“);

        System.out.println(sb);//raj

        System.out.println(sb==sb1);//true

    }

}

StringBuilder

It is mutable, not thread safe.

public class StringAndStringBuffer{

    public static void main(String args[]){

        String s1=”hello”;

        String s2=s1.concat(“world“);

        System.out.println(s1);//hello

        System.out.println(s2);//helloworld (new object created)

        StringBuilder sb=new StringBuilder(“raj“);

        StringBuilder sb1=sb.append(“yadav“);

        System.out.println(sb);//raj

        System.out.println(sb==sb1);//true

    }

}