Small Programs using Java

1. How to find the minimum value in a list?

Primitive: 

List<Integer> lst = Arrays.asList(1, 2, 3, 4, 56, 7, 89, 10);

System.out.println(Collections.min(lst));

Object:

List<Employee> lst = new ArrayList<Employee>();

lst.add(new Employee(10, "Raghu", 25000));

lst.add(new Employee(120, "Krish", 45000));

lst.add(new Employee(210, "John", 14000));

Employee minSal = Collections.min(lst, new EmpComp());

System.out.println(minSal);

 

class EmpComp implements Comparator<Employee>{ 

    public int compare(Employee e1, Employee e2) {

        return e1.getSalary().compareTo(e2.getSalary());

    }

}

Stream

lst.stream.min((e1, e2) -> e1.getSalary().compareTo(e2.getSalary())).get();

2. How to get a list sorted?

Primitive: 

Collections.sort(lst));

Object:

Collections.sort(lst, new EmpComp());

Stream:

lst.stream.sorted((e1, e2) -> e1.getSalary().compareTo(e2.getSalary())).collect(Collectors.toList()); 

Reverse Order:

Collections.sort(lst, Collections.reverseOrder());  

lst.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());

3. How to reverse a String?

Char Array:

Scanner scanner = new Scanner(System.in);

String str = scanner.nextLine();

char[] arr = str.toCharArray();

for (int i = arr.length - 1; i >= 0; i--)

System.out.print(arr[i]);

StringBuilder:

StringBuilder sb = new StringBuilder(str);

sb.reverse().toString();

Arraylist:

List<Character> lst = new ArrayList<>();

for (char c : str)

    lst.add(c);

Collections.reverse(lst);

Stream:

Stream.of(str)

      .map(word->new StringBuilder(word).reverse().toString())

      .collect(Collectors.joining(" ")).get(0);

Stream with index:

char[] arr = str.toCharArray();

IntStream.range(0, arr.length)

        .mapToObj(i -> arr[(arr.length - 1) - i])

        .forEach(System.out::print);

A String is a palindrome if the String is same as the Reversed String.

4. How to search an element?

In String:

if(str.indexOf("word") > -1)

In Arraylist of Primitives:

boolean found = lst.contains(2);

In Arraylist of Objects:

for (Employee emp : emplist) {

    if (emp.getName().equals(name)) {

        return emp;

    }

}

Using Stream:

Employee empl = emplist.stream()

  .filter(emp -> name.equals(emp.getName()))

  .findAny()

  .orElse(null);

5. How to count the occurrences? 

String:

Linear search:

for (int i=0; i<str.length(); i++){

    if (s.charAt(i) == c)

        count++;

    }

return count;

Binary Search:

while (low <= high) {

        mid = (low + high) / 2;

        if (a[mid].compareTo(x) < 0) {

            low = mid + 1;

        } else if (a[mid].compareTo(x) > 0) {

            high = mid - 1;

        } else {

            return mid;

        }

    }

Arraylist:

Collections.frequency(list, new Employee(321222, "John", 29)); 

public boolean equals(Employee e) {

    if(this.id.equals(e.getId()) && this.name.equals(e.getName())) {

        return true;

    }

    return false;

}

Stream:

lst.stream().filter(str -> str.indexOf("ch") > -1).count();

To get count of each item,

lst.stream().collect(Collectors.groupingBy(Function.identity(),Collectors.counting()));

6. How to replace an element?

String:

str.replace('h', 'm');

Arraylist

Collections.replaceAll(lst, null, " ");

Stream:

List<String> newList = lst.stream()

                .map(s -> s != null ? s : "")

                .collect(Collectors.toList());