boomerang.results

Class NullPointer

java.lang.Object

boomerang.results.NullPointer

public class NullPointer
extends Object

Constructor Summary

Constructors

Constructor and Description
NullPointer(Statement statement)
NullPointer(Statement sourceStatement, Val sourceVariable, Statement statement, Val variable, PAutomaton<Statement,INode<Val>> openingContext, PAutomaton<Statement,INode<Val>> closingContext)

Method Summary

Modifier and Type	Method and Description
PAutomaton<Statement,INode<Val>>	getClosingContext() The closing context of a NullPointer provides the call stack via which a variable containing null returns to a caller.
soot.SootMethod	getMethod() Returns the method of the statement at which the null pointer occurs.
PAutomaton<Statement,INode<Val>>	getOpeningContext() The opening context of a NullPointer provides the call stack under which the null pointer occurs.
Statement	getSourceStatement() The source statement of the data-flow, i.e., the statement that assigns null to a variable.
Val	getSourceVariable() The source variable at the source statement.
Statement	getStatement() The statement at which a null pointer occurred.
Val	getVariable() The variable that contains "null" and which provokes at the statement a NullPointerException.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

NullPointer

public NullPointer(Statement statement)

NullPointer

public NullPointer(Statement sourceStatement,
                   Val sourceVariable,
                   Statement statement,
                   Val variable,
                   PAutomaton<Statement,INode<Val>> openingContext,
                   PAutomaton<Statement,INode<Val>> closingContext)

Method Detail

getVariable

public Val getVariable()

The variable that contains "null" and which provokes at the statement a NullPointerException.

Returns:

the variable that contains a null pointer

getStatement

public Statement getStatement()

The statement at which a null pointer occurred. A null pointer can occur at three different types of statements: y = x.toString(); or y = lengthof(x); or y = x.f;

Returns:

the statement where the respective getVariable is null

getSourceStatement

public Statement getSourceStatement()

The source statement of the data-flow, i.e., the statement that assigns null to a variable. Examples are: x = null or x = System.getProperty(...).

Returns:

The source statement of the data-flow/null pointer.

getSourceVariable

public Val getSourceVariable()

The source variable at the source statement. At a statement x = null or x = System.getProperty, this will be the variable x.

Returns:

The source variable of the data-flow propagation

getMethod

public soot.SootMethod getMethod()

Returns the method of the statement at which the null pointer occurs.

Returns:

The SootMethod of the null pointer statement

getOpeningContext

public PAutomaton<Statement,INode<Val>> getOpeningContext()

The opening context of a NullPointer provides the call stack under which the null pointer occurs.

 main(){
        Object x = null;
        foo(x); //call site context "c1"
        Object y = new Object();
        foo(y); //call site context "c2"
 }
 foo(Object z){
        z.toString() // Variable z is null here under context c1, but *not* under c2)
 }
 

In the example above, z is null under the calling context of call site c1. In the case of branching, there can be multiple call site contexts leading to a null pointer. Therefore, the opening context is represented as an automaton (or graph). The edges of the automaton are labeled by the call sites, the nodes are labeled by variables or by variables at a context. For the example above, the automaton contains a transition with label foo(x)

Returns:

The automaton representation of the opening context.

getClosingContext

public PAutomaton<Statement,INode<Val>> getClosingContext()

The closing context of a NullPointer provides the call stack via which a variable containing null returns to a caller.

 main(){
        Object x;
  if(...){
                x = returnNull(); //b1
  } else {
        x = returnNotNull(); //b2
  }
        x.toString() // Variable x is null here when the program executes along branch b1
 }
 Object returnNull(){
        Object y = null;
  return y;
 }
 

In the case above, a null pointer exception occurs when the program executes along branch b1. There can be multiple contexts leading to a null pointer. Therefore, the closing context is represented as an automaton (or graph). The edges of the automaton are labeled by the call sites, the nodes are labeled by variables or by variables at a context. For the example above, the automaton contains a transition with label returnNull(). This indicates, that the null pointer only occurs along branch b1 but not b2.

Returns:

The automaton representation of the closing context.

toString

public String toString()

Overrides:

toString in class Object