Java Instanceof

objectReference instanceof Type

Object obj = new ArrayList<String>();

// boolean isStringList = obj instanceof List<String>; // Compile-time error
boolean isList = obj instanceof List<?>;               // Valid: unbounded wildcard
boolean isRawList = obj instanceof List;               // Valid: raw type

Number num = Integer.valueOf(42);

boolean isInteger = num instanceof Integer; // true: runtime type is Integer
boolean isNumber  = num instanceof Number;  // true: Integer is a subtype of Number
boolean isObject  = num instanceof Object;  // true: Integer inherits from Object
boolean isDouble  = num instanceof Double;  // false: runtime type is Integer, not Double
boolean isNull    = null instanceof String; // false: null references always return false

String text = "Java";
// boolean isInt = text instanceof Integer; // Compile-time error: inconvertible types

objectReference instanceof Type patternVariable

Object obj = "Technical Documentation";

// 'str' is only in scope if the evaluation is true
if (obj instanceof String str) {
    int len = str.length(); // No explicit cast required
}

// 'str' is out of scope here

// Valid: 'str' is guaranteed to be bound if the right side evaluates
if (obj instanceof String str && str.length() > 5) {
    // ...
}

// Compile-time error: 'str' might not be bound if the left side is false
// if (obj instanceof String str || str.length() > 5) { ... }