Muhammet Esat BÜYÜKBULUT

Basics

—

by

Muhammet Esat BÜYÜKBULUT
in

Installation

  1. Install JDK 17 (LTS)
  2. Install IntelliJ IDEA Community

Conditional Statements

If, else if, else

public static void main(String[] args) {
    int grade = 75;

    if (grade>50){
        System.out.println("Success");
    }else if (grade > 25){
        System.out.println("Conditional success");
    }else{
        System.out.println("Fail");
    }
}

switch case

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        int num;
        Scanner scanner = new Scanner(System.in);
        System.out.println("---MENU---\n1 - Play\n2 - Options\n3 - Exit");
        num = scanner.nextInt();
    
        switch (num){
            case 1: System.out.println("Playing..."); break;
            case 2: System.out.println("Options..."); break;
            case 3: System.out.println("Good bye!"); break;
            default: System.out.println("Oh! I don't understand.");
        }
    }
}

Loops

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        int counter = 0;
        while (counter<10){
            System.out.print(counter + ", ");
            counter++;
        } // 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 
 
        System.out.println("\n");

        for(int j = 0; j < 100; j++){
            if(j%3==0 && j%7==0)
                System.out.print(j + ", ");
        } // 0, 21, 42, 63, 84, 
    }
}

Strings

Strings are immutable

String Constructs

// String Constructs
String str1 = "JAVA";
String str2 = new String("JAVA");

char c[]={'h','e','l','l','o'};
String str3 = new String(c,1,2);

byte b[]={65,66,67,68};
String str4 = new String(b, 1,2);

System.out.println(str1); // JAVA
System.out.println(str2); // JAVA
System.out.println(str3); // el
System.out.println(str4); // BC

String Pooling

Java can hold same data in same memory position. == operator compare values of referances NOT actual text.

// Java string pooling
String comp1 = "JAVA";
String comp2 = "JAVA";
String comp3 = new String("JAVA");

System.out.println("\n\nString Pooling");
System.out.println(comp1 == comp2); // true
System.out.println(comp1 == comp3); // false

String Methods

// JAVA String Methods
String m1 = "java".toUpperCase();  //JAVA
String m2 = "JAVA".toLowerCase();  //java
String m3 = "    java     ".trim();  //java
String m4 = "java".substring(2);  //va
String m5 = "Hello java".substring(3,4);  //l
String m6 = "Hello java".replace('a','e');  //Hello jeve
Boolean m7 = "Hello java".startsWith("He");  //true
Boolean m8 = "Hello java".endsWith("va");  //true
char m9 = "Hello Java".charAt(4);  //o
int m10 = "Hello dear java user".indexOf("dear");  //6
int m11 = "Hello dear java user".indexOf('w');  //-1
int m12 = "Hello dear java user".indexOf('a');  //8
int m13 = "Hello dear java user".indexOf("a",10);  //12
int m14 = "Hello dear java user".lastIndexOf("a");  //14
boolean m15 = "java".equals("java");  //true
boolean m16 = "java".equals("JAVA");  //false
boolean m17 = "java".equalsIgnoreCase("JAVA");  //true
int m18 = "aa".compareTo("bb");  //-1
int m19 = "aa".compareTo("aa");  //0
int m20 = "bb".compareTo("aa");  //1
String m21 = String.valueOf(23.2);  //23.2


System.out.println("\n\nString Methods");
System.out.println(m1);   // JAVA
System.out.println(m2);   // java
System.out.println(m3);   // java
System.out.println(m4);   // va
System.out.println(m5);   // l
System.out.println(m6);   // Hello jeve
System.out.println(m7);   // true
System.out.println(m8);   // true
System.out.println(m9);   // o
System.out.println(m10);  // 6
System.out.println(m11);  // -1
System.out.println(m12);  // 8
System.out.println(m13);  // 12
System.out.println(m14);  // 14
System.out.println(m15);  // true
System.out.println(m16);  // false
System.out.println(m17);  // true
System.out.println(m18);  // -1
System.out.println(m19);  // 0
System.out.println(m20);  // 1
System.out.println(m21);  // 23.2

Regex

// Regex
boolean reg1 = "a123b".matches(".123b");    // true
boolean reg2 = "a123b".matches("[^b]\\w*"); // true

System.out.println(reg1); // true
System.out.println(reg2); // true


// Characters
// x	The character x
// \\	The backslash character
// \0n	The character with octal value 0n (0 <= n <= 7)
// \0nn	The character with octal value 0nn (0 <= n <= 7)
// \0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
// \xhh	The character with hexadecimal value 0xhh
// \\uhhhh	The character with hexadecimal value 0xhhhh
// \x{h...h}	The character with hexadecimal value 0xh...h (Character.MIN_CODE_POINT  <= 0xh...h <=  Character.MAX_CODE_POINT)
// \t	The tab character ('\\u0009')
// \n	The newline (line feed) character ('\\u000A')
// \r	The carriage-return character ('\\u000D')
// \f	The form-feed character ('\u000C')
// \a	The alert (bell) character ('\u0007')
// \e	The escape character ('\u001B')
// \cx	The control character corresponding to x
//
// Character classes
// [abc]	a, b, or c (simple class)
// [^abc]	Any character except a, b, or c (negation)
// [a-zA-Z]	a through z or A through Z, inclusive (range)
// [a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
// [a-z&&[def]]	d, e, or f (intersection)
// [a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
// [a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)
//
// Predefined character classes
// .	Any character (may or may not match line terminators)
// \d	A digit: [0-9]
// \D	A non-digit: [^0-9]
// \s	A whitespace character: [ \t\n\x0B\f\r]
// \S	A non-whitespace character: [^\s]
// \w	A word character: [a-zA-Z_0-9]
// \W	A non-word character: [^\w]
// https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html

Arrays

public class Main {
    public static void main(String[] args) {
        //ARRAYS
        // Construct
        int A[] = new int[5];
        int B[] = {2,3,5,7,12,12,13};
        System.out.println(A.length);
        System.out.println(B.length);

        // Jagged array
        int j[][]=new int[4][];
        j[0] = new int[5];
        j[1] = new int[3];
        j[2] = new int[6];
        j[3] = new int[2];

        // foreach
        for(int row[]:j) {
            for (int elem : row)
                System.out.print("*");
            System.out.print("\n");
        }

    }
}

Methods

Static & Non-Static Methods

public class Main {
    public static int max(int x, int y){
        return x>y ? x : y;
    }
    public int min(int x, int y){
        return x<y ? x : y;
    }
    public static void main(String[] args) {
        // We can call static methods without creating an object
        System.out.println(max(10,15)); // 15

        // We have to create an object for calling non-static methods
        Main obj = new Main();
        System.out.println(obj.min(10,15)); // 10
    }
}

Passing Array

We copy array reference

public class Main {

    public static void PrintArray(int arr[]){
        for (int i : arr) System.out.printf(i + ", ");
        System.out.println();
    }

    public static void FillArray(int arr[], int vaule){
        for (int i = 0; i<arr.length; i++) arr[i] = vaule;
    }

    public static void main(String[] args) {
        int A[] = {1,5,6,2,23,41};
        PrintArray(A);
        FillArray(A,25);
        PrintArray(A);
    }
}

Pass by Referance & Pass by Pointer

There isn’t exits such a content in JAVA. You can only pass by value(copy).

https://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value

Method Overloading

public class Main {

    public static int max(int x, int y){
        return x>y ? x : y;
    }
    public static float max(float x, float y){
        return x>y ? x : y;
    }


    public static void main(String[] args) {
        System.out.println(max(3,5));        // 5
        System.out.println(max(33.3f,5.1f)); // 33.3
    }
}

Variable argument

public static void MyPrint(int ... nums){
        for (int i : nums) System.out.printf(i + ", ");
        System.out.println();
    }


    public static void main(String[] args) {
        MyPrint(1,4,2,5,6,234,1,23,5,6);
    }

Comments

Leave a Reply

Your email address will not be published. Required fields are marked *