C++ vs. Java: Similiarities & Differences Dr. Jeyakesavan Veerasamy Director of CS UTDesign program & CS Teaching Faculty University of Texas at Dallas, USA

History C (1969)  C++ (1979)  Java (1995) Both support OOP. Most OOP library contents are similar, however Java continues to grow. Syntax is very close – Java has strong influence of C/C++. Easy to learn the other language when you know one of these.

C++ compiler & Linker usage file1.cppfile2.cppfilen.cpp …. file1.ofile2.ofilen.o …. Linker application (executable) Compiler C++ compiler does not care about filenames. This appliction runs directly on top of OS.

Java compiler usage file1.javafile2.javafilen.java …. file1.classfile2.classfilen.class …. Compiler Operating System Java Runtime Environment (JRE)

C++ vs. Java: differences C++Java Write once, compile everywhere  unique executable for each target Write once, run anywhere  same class files will run above all target-specific JREs. No strict relationship between class names and filenames. Typically, a header file and implementation file are used for each class. Strict relationship is enforced, e.g. source code for class PayRoll has to be in PayRoll.java

C++ vs. Java: differences … C++Java I/O statements use cin and cout, e.g. cin >> x; cout << y; I/O input mechanism is bit more complex, since default mechanism reads one byte at a time (System.in). Output is easy, e.g. System.out.println(x); Pointers, References, and pass by value are supported. No array bound checking. Primitive data types always passed by value. Objects are passed by reference. Array bounds are always checked.

C++ vs. Java: differences … C++Java Explicit memory management. Supports destructors. Automatic Garbage Collection. Supports operator overloading. Specifically operator overloading was thrown out.

Types of memory used by executable task Code Stack data (static) heap (dynamic)

Objects Objects can be created as local variables just like any basic data types in C++. C++: ComplexType num1; Java: Nothing equivalent – Objects cannot be in stack.

Objects in Heap C++: ComplexType *num1 = new ComplexType(…); Java: ComplexType num1 = new ComplexType(…);

Arrays Basic data types and classes are treated the same way in C++, unlike Java. C++: ComplexNumber numbers[5]; Java: nothing equivalent.

C++ array version #2 ComplexNumber *numbers; numbers = new ComplexNumber[5]; Java: nothing equivalent for classes, but possible for basic data types: int numbers[]; numbers = new int[5];

C++ array version #3 ComplexNumber **numbers; numbers = new ComplexNumber*[5]; for( index i = 0 ; i < 5 ; i++) numbers[i] = new ComplexNumber(…); Java: ComplexNumber numbers[]; numbers = new ComplexNumber [5]; for( index i = 0 ; i < 5 ; i++) numbers[i] = new ComplexNumber(…);

C++ vs. Java: Analogy Working with C++ is like flying a airpline, while working with Java is like driving a car. What does it mean? Too many controls/options in C++: think before use each one. Careful use can result in efficiency, poor use can result in serious inefficiency Issues like memory leak can crash the application, out-of-bounds array access can cause memory corruption – but it may not show up for long time – causing lot of headache! Java : slow and steady wins the race?

References C++ tutorials: C++ reference: Java tutorial: Java API documentation: