Bubble sort and selection sort for ICSE Class 10, traced pass by pass.

import java.util.Scanner;
class SelectDesc {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int a[] = new int[6];
        System.out.println("Enter 6 scores:");
        for (int i = 0; i < 6; i++)
            a[i] = sc.nextInt();
        for (int i = 0; i < 5; i++) {
            int big = i;                           // position of the largest so far
            for (int j = i + 1; j < 6; j++)
                if (a[j] > a[big])
                    big = j;
            int t = a[i];                          // one swap per pass
            a[i] = a[big];
            a[big] = t;
            System.out.print("Pass " + (i + 1) + " (largest at index " + big + "):");
            for (int k = 0; k < 6; k++)
                System.out.print(" " + a[k]);
            System.out.println();
        }
    }
}

For ascending order, look for the smallest instead: change > to < in the comparison and rename big to small.

import java.util.Scanner;
class SortNames {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        String nm[] = new String[6];
        System.out.println("Enter 6 names:");
        for (int i = 0; i < 6; i++)
            nm[i] = sc.next();
        for (int i = 0; i < 5; i++)
            for (int j = 0; j < 5 - i; j++)
                if (nm[j].compareToIgnoreCase(nm[j + 1]) > 0) {
                    String t = nm[j];
                    nm[j] = nm[j + 1];
                    nm[j + 1] = t;
                }
        System.out.println("In alphabetical order:");
        for (int i = 0; i < 6; i++)
            System.out.println(nm[i]);
    }
}

compareToIgnoreCase returns a positive number when the left word comes later in the alphabet, so > 0 plays the part of > in a number sort.

Enter 6 names:
Zoya aarav Meera Kabir neel Ishaan
In alphabetical order:
aarav
Ishaan
Kabir
Meera
neel
Zoya

Variables: nm String[] names; i, j int pass and position; t String temporary. With plain compareTo the small-letter names would sort after Zoya, because small letters have higher codes.

import java.util.Scanner;
class MeritList {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        String name[] = new String[5];
        int marks[] = new int[5];
        System.out.println("Enter name and marks of 5 students:");
        for (int i = 0; i < 5; i++) {
            name[i] = sc.next();
            marks[i] = sc.nextInt();
        }
        for (int i = 0; i < 4; i++) {
            int big = i;
            for (int j = i + 1; j < 5; j++)
                if (marks[j] > marks[big])
                    big = j;
            int t = marks[i]; marks[i] = marks[big]; marks[big] = t;
            String s = name[i]; name[i] = name[big]; name[big] = s;   // move the name with its marks
        }
        System.out.println("Rank\tName\tMarks");
        for (int i = 0; i < 5; i++)
            System.out.println((i + 1) + "\t" + name[i] + "\t" + marks[i]);
    }
}

Whatever swap is made in marks must be made in name at the same two indices, or names and marks drift apart.

Enter name and marks of 5 students:
Tara 78 Dev 91 Anya 66 Rohan 84 Sana 91
Rank	Name	Marks
1	Dev	91
2	Sana	91
3	Rohan	84
4	Tara	78
5	Anya	66

Variables: name String[], marks int[]; i, j, big int; t int and s String temporaries. Dev stays ahead of Sana because the strict > does not move an equal mark.

import java.util.Scanner;
class RollSearch {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int roll[] = new int[8];
        System.out.println("Enter 8 roll numbers in ascending order:");
        for (int i = 0; i < 8; i++)
            roll[i] = sc.nextInt();
        // check the order first: binary search is only valid on sorted data
        boolean sorted = true;
        for (int i = 0; i < 7; i++)
            if (roll[i] > roll[i + 1])
                sorted = false;
        if (!sorted) {
            System.out.println("Roll numbers are not in ascending order");
            return;
        }
        System.out.print("Roll number to find: ");
        int key = sc.nextInt();
        int low = 0, high = 7, steps = 0, pos = -1;
        while (low <= high) {
            int mid = (low + high) / 2;
            steps++;
            if (roll[mid] == key) { pos = mid; break; }
            if (roll[mid] < key) low = mid + 1;
            else high = mid - 1;
        }
        if (pos >= 0)
            System.out.println("Present at position " + (pos + 1) + " after " + steps + " comparisons");
        else
            System.out.println("Absent, decided after " + steps + " comparisons");
    }
}

The order check costs seven comparisons and saves a wrong answer: binary search on unsorted data can miss a value that is there.

Enter 8 roll numbers in ascending order:
3 7 12 18 21 25 30 34
Roll number to find: 25
Present at position 6 after 2 comparisons

Enter 8 roll numbers in ascending order:
3 7 12 18 21 25 30 34
Roll number to find: 4
Absent, decided after 3 comparisons

Enter 8 roll numbers in ascending order:
3 7 12 9 21 25 30 34
Roll numbers are not in ascending order

Variables: roll int[]; sorted boolean; key, low, high, mid, steps, pos int.

import java.util.Scanner;
class MaxMinAvg {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        double t[] = new double[7];
        System.out.println("Enter the maximum temperature for 7 days:");
        for (int i = 0; i < 7; i++)
            t[i] = sc.nextDouble();
        double max = t[0], min = t[0], sum = 0;
        int hot = 0;                               // day number of the hottest day
        for (int i = 0; i < 7; i++) {
            sum = sum + t[i];
            if (t[i] > max) { max = t[i]; hot = i; }
            if (t[i] < min) min = t[i];
        }
        double avg = sum / 7;
        int above = 0;
        for (int i = 0; i < 7; i++)
            if (t[i] > avg) above++;
        System.out.println("Highest = " + max + " on day " + (hot + 1));
        System.out.println("Lowest = " + min);
        System.out.println("Average = " + Math.round(avg * 100) / 100.0);
        System.out.println("Days above average = " + above);
    }
}

max and min start at t[0], not at 0: a week of temperatures all below 0 would otherwise report a maximum of 0.

Enter the maximum temperature for 7 days:
31.5 33 29.5 35.5 34 30 32
Highest = 35.5 on day 4
Lowest = 29.5
Average = 32.21
Days above average = 3

Variables: t double[]; max, min, sum, avg double; hot, above, i int. The average needs the whole first pass, so counting days above it needs a second loop.