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Type Inference Summary

Type Inference Concept

  • Compiler determines types automatically
  • Reduces verbosity in generic code
  • Based on context and type constraints
  • Example: 
    // Without type inference
List<String> list = new ArrayList<String>();

// With type inference
List<String> list = new ArrayList<>();  // diamond operator

Diamond Operator

  • Used in constructor calls
  • Infers type from declaration
  • Example: 
    Map<String, List<Integer>> map = new HashMap<>();
Pair<Double, String> pair = new Pair<>();

Method Type Inference

  • Infers type arguments for generic methods
  • Based on:
    • Method arguments
    • Return type context
    • Type constraints
  • Example: 
    static <T> List<T> asList(T... elements) {
  return Arrays.asList(elements);
}

List<String> list = asList("a", "b", "c");  // T inferred as String

Target Typing

  • Uses assignment context for inference
  • Considers variable type
  • Example: 
    List<String> strings = Collections.emptyList();  // infers List<String>
void process(List<Integer> ints) { }
process(Collections.emptyList());  // infers List<Integer>

Type Inference Rules

  • Most specific type is chosen
  • Must satisfy all constraints
  • Example: 
    // T must be supertype of both String and Integer
<T> void addToList(List<T> list, T item1, T item2) { }
List<Object> list = new ArrayList<>();
addToList(list, "hello", 42);  // T inferred as Object

Best Practices

  • Use diamond operator
  • Let compiler infer types when clear
  • Provide explicit types when needed
  • Test inference with edge cases
  • Document when inference is complex
  • Consider readability vs brevity