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Language Beginner

Diamond with anonymous classes

Diamond operator now works with anonymous classes too.

Generics

Code Comparison

✕ Java 7/8

Map<String, List<String>> map =
    new HashMap<String, List<String>>();
// anonymous class: no diamond
Predicate<String> p =
    new Predicate<String>() {
        public boolean test(String s) {..}
    };

✓ Java 9+

Map<String, List<String>> map =
    new HashMap<>();
// Java 9: diamond with anonymous classes
Predicate<String> p =
    new Predicate<>() {
        public boolean test(String s) {..}
    };

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Why the modern way wins

📏

Consistent rules

Diamond works everywhere — constructors and anonymous classes alike.

🧹

Less redundancy

Type arguments are stated once on the left, never repeated.

🔧

DRY principle

The compiler already knows the type — why write it twice?

Old Approach

Repeat Type Args

Modern Approach

Diamond <>

Since JDK

Difficulty

Beginner

JDK Support

Diamond with anonymous classes

Available

Diamond with anonymous classes since JDK 9 (Sept 2017).

How it works

Java 7 introduced <> but it didn't work with anonymous inner classes. Java 9 fixed this, so you never need to repeat type arguments on the right-hand side.

Type inference with var

Java 8

Map<String, List<Integer>> map =
    new HashMap<String, List<Integer>>();
for (Map.Entry<String, List<Integer>> e
    : map.entrySet()) {
    // verbose type noise
}

Java 10+

var map = new HashMap<String, List<Integer>>();
for (var entry : map.entrySet()) {
    // clean and readable
}

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JDK 10+ →

Language Beginner

Text blocks for multiline strings

Java 8

String json = "{\n" +
    "  \"name\": \"Duke\",\n" +
    "  \"age\": 30\n" +
    "}";

Java 15+

String json = """
    {
      "name": "Duke",
      "age": 30
    }""";

Hover to see modern ➜

JDK 15+ →

Language Beginner

Switch expressions

Java 8

String msg;
switch (day) {
    case MONDAY:
        msg = "Start";
        break;
    case FRIDAY:
        msg = "End";
        break;
    default:
        msg = "Mid";
}

Java 14+

String msg = switch (day) {
    case MONDAY  -> "Start";
    case FRIDAY  -> "End";
    default      -> "Mid";
};

Hover to see modern ➜

JDK 14+ →