النصوص والمحارف

public class Positions {
    public static void main(String[] args) {
        String name = "Sara";
        System.out.println(name.length());
        System.out.println(name.charAt(0));
        System.out.println(name.charAt(1));
        System.out.println(name.charAt(name.length() - 1));
    }
}

4
S
a
a

public class OutOfRange {
    public static void main(String[] args) {
        String name = "Sara";
        System.out.println(name.charAt(3));
        System.out.println(name.charAt(name.length()));
        System.out.println("This line never runs");
    }
}

a

public class ArabicText {
    public static void main(String[] args) {
        String name = "سارة";
        System.out.println(name);
        System.out.println(name.length());
        System.out.println(name.charAt(0));
        System.out.println(name.contains("ار"));
        System.out.println(name + " تتعلم Java");
    }
}

سارة
4
س
true
سارة تتعلم Java

public class EmailSearch {
    public static void main(String[] args) {
        String email = "sara.ali@ucas.edu.ps";
        int at = email.indexOf("@");
        System.out.println(at);
        System.out.println(email.substring(0, at));
        System.out.println(email.substring(at + 1));
        System.out.println(email.contains("ucas"));
        System.out.println(email.startsWith("sara"));
        System.out.println(email.endsWith(".com"));
        System.out.println(email.indexOf("#"));
    }
}

8
sara.ali
ucas.edu.ps
true
true
false
-1

public class CleanText {
    public static void main(String[] args) {
        String raw = "  Hello World  ";
        System.out.println("[" + raw.trim() + "]");
        System.out.println("[" + raw.trim().toLowerCase() + "]");
        System.out.println("[" + raw.replace("World", "Java") + "]");
        System.out.println("banana".replace("a", "o"));
        System.out.println("[" + raw + "]");
    }
}

[Hello World]
[hello world]
[  Hello Java  ]
bonono
[  Hello World  ]

public class CompareStrings {
    public static void main(String[] args) {
        System.out.println("java".equals("Java"));
        System.out.println("java".equalsIgnoreCase("Java"));
        System.out.println("apple".compareTo("banana"));
        System.out.println("banana".compareTo("apple"));
        System.out.println("apple".compareTo("apple"));
        System.out.println("Zed".compareTo("apple"));
    }
}

false
true
-1
1
0
-7

import java.util.Arrays;

public class SortNames {
    public static void main(String[] args) {
        String[] names = {"Sara", "Ali", "Huda"};
        for (int i = 0; i < names.length - 1; i++) {
            for (int k = 0; k < names.length - 1 - i; k++) {
                if (names[k].compareTo(names[k + 1]) > 0) {
                    String temp = names[k];
                    names[k] = names[k + 1];
                    names[k + 1] = temp;
                }
            }
        }
        System.out.println(Arrays.toString(names));
    }
}

[Ali, Huda, Sara]

public class SplitBasics {
    public static void main(String[] args) {
        String line = "Sara,19,3.75";
        String[] parts = line.split(",");
        System.out.println(parts.length);
        for (int i = 0; i < parts.length; i++) {
            System.out.println(i + ": " + parts[i]);
        }
    }
}

3
0: Sara
1: 19
2: 3.75

public class SplitPatterns {
    public static void main(String[] args) {
        String text = "  one   two three ";
        System.out.println(text.split(" ").length);
        System.out.println(text.trim().split("\\s+").length);
        System.out.println("3.75".split(".").length);
        System.out.println("3.75".split("\\.").length);
    }
}

7
3
0
2

public class CountVowels {
    public static void main(String[] args) {
        String text = "Programming in Java".toLowerCase();
        int count = 0;
        for (int i = 0; i < text.length(); i++) {
            char c = text.charAt(i);
            if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') {
                count++;
            }
        }
        System.out.println("Vowels: " + count);
    }
}

Vowels: 6

public class ReverseText {
    public static String reverse(String text) {
        String reversed = "";
        for (int i = text.length() - 1; i >= 0; i--) {
            reversed = reversed + text.charAt(i);
        }
        return reversed;
    }

    public static void main(String[] args) {
        System.out.println(reverse("Java"));
        System.out.println(reverse("رادار").equals("رادار"));
    }
}

avaJ
true

public class CharKinds {
    public static void main(String[] args) {
        String text = "Room 12B!";
        int letters = 0;
        int digits = 0;
        int others = 0;
        for (int i = 0; i < text.length(); i++) {
            char c = text.charAt(i);
            if (Character.isLetter(c)) {
                letters++;
            } else if (Character.isDigit(c)) {
                digits++;
            } else {
                others++;
            }
        }
        System.out.println("Letters: " + letters);
        System.out.println("Digits: " + digits);
        System.out.println("Others: " + others);
    }
}

Letters: 5
Digits: 2
Others: 2

public class ParseNumbers {
    public static void main(String[] args) {
        String age = "19";
        System.out.println(age + 1);
        int years = Integer.parseInt(age);
        System.out.println(years + 1);
        double gpa = Double.parseDouble("3.75");
        System.out.println(gpa * 2);
    }
}

191
20
7.5

public class ParseCrash {
    public static void main(String[] args) {
        System.out.println("Before");
        int n = Integer.parseInt("abc");
        System.out.println(n);
    }
}

Before

public class ParseTry {
    public static void main(String[] args) {
        String[] inputs = {"42", "3.5", "abc", " 7", ""};
        for (String text : inputs) {
            try {
                int n = Integer.parseInt(text);
                System.out.println("OK: " + n);
            } catch (NumberFormatException e) {
                System.out.println(e.getMessage());
            }
        }
    }
}

OK: 42
For input string: "3.5"
For input string: "abc"
For input string: " 7"
For input string: ""

public class BuilderLine {
    public static void main(String[] args) {
        StringBuilder line = new StringBuilder();
        for (int i = 1; i <= 5; i++) {
            line.append(i);
            if (i < 5) {
                line.append(", ");
            }
        }
        String result = line.toString();
        System.out.println(result);
        System.out.println(result.length());
    }
}

1, 2, 3, 4, 5
13

public class CsvParser {
    public static void main(String[] args) {
        String[] lines = {"Sara Ali, 19, 3.75", "Omar, 20, 2.5"};
        for (String line : lines) {
            String[] parts = line.split(",");
            String name = parts[0].trim();
            int age = Integer.parseInt(parts[1].trim());
            double gpa = Double.parseDouble(parts[2].trim());
            System.out.printf("%-10s %3d %5.2f%n", name, age + 1, gpa);
        }
    }
}

Sara Ali    20  3.75
Omar        21  2.50

public class CaesarLab {
    public static String encrypt(String text, int key) {
        StringBuilder out = new StringBuilder();
        for (int i = 0; i < text.length(); i++) {
            char c = text.charAt(i);
            if (c >= 'a' && c <= 'z') {
                out.append((char) ('a' + (c - 'a' + key) % 26));
            } else {
                out.append(c);
            }
        }
        return out.toString();
    }

    public static void main(String[] args) {
        String secret = encrypt("lazy zebra", 3);
        System.out.println(secret);
        System.out.println(encrypt(secret, 26 - 3));
    }
}

odcb cheud
lazy zebra