Collections

public static ArrayList<Integer> a(ArrayList<Integer> a) {

    ArrayList<Integer> b = new ArrayList<>();

    for (int d = 0; d < a.size(); d++) {
        int c = a.get(d);
        if (c % 2 == 0) {
            b.add(c);
        }
    }

    return b;
}

ArrayList<Integer> a = new ArrayList<>();
a.add(1);
a.add(2);
a.add(3);
a.add(4);
a.add(5);
a.add(6);

ArrayList<Integer> b = a(a);
System.out.println("Even numbers: " + b);

import java.util.HashSet;
import java.util.Set;

Set<Integer> i(Set<Integer> a, Set<Integer> b) {
    Set<Integer> r = new HashSet<>();
    for (Integer x : a) {
        if (b.contains(x)) {
            r.add(x);
        }
    }
    return r;
}

Set<Integer> a = new HashSet<>();
a.add(1);
a.add(2);
a.add(3);

Set<Integer> b = new HashSet<>();
b.add(2);
b.add(3);
b.add(4);

Set<Integer> r = i(a, b);
System.out.println(r);

import java.util.ArrayDeque;
import java.util.Deque;

Deque<String> ℓ = new ArrayDeque<>();

ℓ.addLast("Alice");
ℓ.addLast("Bob");
ℓ.addLast("Charlie");

ℓ.addFirst("VIP");

ℓ.removeFirst();

System.out.println("Front: " + ℓ.peekFirst());
System.out.println("Back: " + ℓ.peekLast());
System.out.println("Size: " + ℓ.size());

import java.util.HashSet;
import java.util.Random;
import java.util.Set;

Set<Integer> s = new HashSet<>();
Random r = new Random();

while (s.size() < 10) {
    int i = 1900000 + r.nextInt(100000);
    s.add(i);
}

System.out.println("IDs: " + s);

int x = 1901234;
System.out.println("Has " + x + "? " + s.contains(x));

int a = 1;

public void increment(int b) {
    b += 1;
}

increment(a);
System.out.println(a); // will print out 1

import org.knowm.xchart.*;
import org.knowm.xchart.BitmapEncoder.BitmapFormat;
import java.util.*;
import java.io.*;

// Sample data
List<Integer> xData = Arrays.asList(0, 1, 2, 3, 4);
List<Double> yData = Arrays.asList(2.0, 1.5, 3.0, 2.5, 4.0);

// Create chart
XYChart chart = new XYChartBuilder().width(600).height(400).title("Sample Line Chart").xAxisTitle("X").yAxisTitle("Y").build();
chart.addSeries("My Data", xData, yData);

// Save to byte array output stream
ByteArrayOutputStream baos = new ByteArrayOutputStream();
BitmapEncoder.saveBitmap(chart, baos, BitmapFormat.PNG);

// Return the image bytes for the notebook to display inline
baos.toByteArray();