statements } assert statement assert statements have been available since J2SE 1.4. These types of statements are used to make assertions in the source code, which can be turned on and off during execution for specific classes or packages. To declare an assertion the assert keyword is used followed by a conditional expression. If it evaluates to false when the statement is executed, an exception is thrown. This statement can include a colon followed by another expression, which will act as the exception's detail message. // If n equals 0, AssertionError is thrown assert n != 0; /* If n equals 0, AssertionError will be thrown with the message after the colon */ assert n != 0 : "n was equal to zero"; Primitive types Primitive types in Java include integer types, floating-point numbers, UTF-16 code units and a boolean type. There are no unsigned types in Java except char type, which is used to represent UTF-16 code units. The lack of unsigned types is offset by introducing unsigned right shift operation (>>>), which is not present in C++. Nevertheless, criticisms have been leveled about the lack of compatibility with C and C++ this causes. char does not necessarily correspond to a single character. It may represent a part of a surrogate pair, in which case Unicode code point is represented by a sequence of two char values. Boxing and unboxing This language feature was introduced in J2SE 5.0. Boxing is the operation of converting a value of a primitive type into a value of a corresponding reference type, which serves as a wrapper for this particular primitive type. Unboxing is the reverse operation of converting a value of a reference type (previously boxed) into a value of a corresponding primitive type. Neither operation requires an explicit conversion. Example: int foo = 42; // Primitive type Integer bar = foo; /* foo is boxed to bar, bar is of Integer type, which serves as a wrapper for int */ int foo2 = bar; // Unboxed back to primitive type Reference types Reference types include class types, interface types, and array types. When the constructor is called, an object is created on the heap and a reference is assigned to the variable. When a variable of an object gets out of scope, the reference is broken and when there are no references left, the object gets marked as garbage. The garbage