How can I create a memory leak in Java?

Question

I just had an interview, and I was asked to create a memory leak with Java.

Needless to say, I felt pretty dumb having no clue on how to eve

Answer 1

Static field holding object reference [esp final field]

class MemorableClass {
    static final ArrayList list = new ArrayList(100);
}

Calling String.intern() on lengthy String

String str=readString(); // read lengthy string any source db,textbox/jsp etc..
// This will place the string in memory pool from which you can't remove
str.intern();

(Unclosed) open streams ( file , network etc... )

try {
    BufferedReader br = new BufferedReader(new FileReader(inputFile));
    ...
    ...
} catch (Exception e) {
    e.printStacktrace();
}

Unclosed connections

try {
    Connection conn = ConnectionFactory.getConnection();
    ...
    ...
} catch (Exception e) {
    e.printStacktrace();
}

Areas that are unreachable from JVM's garbage collector, such as memory allocated through native methods

In web applications, some objects are stored in application scope until the application is explicitly stopped or removed.

getServletContext().setAttribute("SOME_MAP", map);

Incorrect or inappropriate JVM options, such as the noclassgc option on IBM JDK that prevents unused class garbage collection

See IBM jdk settings.