JDK 8 -> 20

Set<String> mySet = new HashSet<String>();mySet.add("yun");mySet.add("yyx");mySet.add("andy");mySet = Collections.unmodifiableSet(mySet);

Set<String> mySet = Set.of("yun", "yyx", "andy");

String str = "https://dev.to/";URL url = new URL(str);URLConnection con = url.openConnection();

var str = "https://dev.to/";var url = new URL(str);var con = url.openConnection();

var flag = 0; // intshortbytevar items = new ArrayList<>(); // ArrayList<Object>

String season;switch(month){    case MAR:    case APR:    case MAY:        season = "spring";        break;    case JUN:    case JUL:    case AUG:        season = "summer";        break;    case SEP:    case OCT:    case NOV:        season = "autumn";        break;    case DEC:    case JAN:    case FEB:        season = "winter";        break;    default:        throw new IllegalArgumentException("Not a month: " + month);}return season;

return switch(month){    case MAR, APR, MAY -> "spring";    case JUN, JUL, AUG -> "summer";    case SEP, OCT, NOV -> "autumn";    case DEC, JAN, FEB -> "winter";}

a.i = b.j;

Exception in thread "main" java.lang.NullPointerException    at App.main(App.java:5)

Exception in thread "main" java.lang.NullPointerException:     Cannot read field "j" because "b" is null    at App.main(App.java:5)

String json = "{
" +    "\"name\": \"" + user.name + "\",
" +    "\"nickname\": \"" + user.nickName + "\"
" +     "}";

var json = """        {            "name": "%s",            "nickname": "%s"        }        """.formatted(user.name, user.nickName);

if( obj instanceof String){ // 1)  obj     // 2) declare  String  str3)  cast obj  String     String str = (String) obj;     //  str }

if( obj instanceof String str ){    //  str }

final class Point {    private final int x;    private final int y;    Point(int x, int y) {        this.x = x;        this.y = y;    }    int x() { return x; }    int y() { return y; }    public boolean equals(Object o) {        if (!(o instanceof Point)) return false;        Point other = (Point) o;        return other.x == x && other.y == y;    }    public int hashCode() {        return Objects.hash(x, y);    }    public String toString() {        return String.format("Point[x=%d, y=%d]", x, y);    }}

@Getter@ToString@EqualsAndHashCode@AllArgsConstructorfinal class Point{    final int x;    final int y;}

record Point(int x, int y) { }

public abstract sealed class Shape    permits Circle, Rectangle, Square, WeirdShape { ... }public final class Circle extends Shape { ... }public sealed class Rectangle extends Shape     permits TransparentRectangle, FilledRectangle { ... }public final class TransparentRectangle extends Rectangle { ... }public final class FilledRectangle extends Rectangle { ... }public final class Square extends Shape { ... }public non-sealed class WeirdShape extends Shape { ... }

static String formatter(Object o) {    String formatted = "unknown";    if (o instanceof Integer i) {        formatted = String.format("int %d", i);    } else if (o instanceof Long l) {        formatted = String.format("long %d", l);    } else if (o instanceof Double d) {        formatted = String.format("double %f", d);    } else if (o instanceof String s) {        formatted = String.format("String %s", s);    }    return formatted;}

static String formatterPatternSwitch(Object o) {    return switch (o) {        case Integer i -> String.format("int %d", i);        case Long l    -> String.format("long %d", l);        case Double d  -> String.format("double %f", d);        case String s  -> String.format("String %s", s);        default        -> o.toString();    };}