What is the difference between displacement and double displacement reactions? Write equations for these reactions.

(N/A) In a displacement reaction,a more reactive element replaces a less reactive element from its compound.
$A + BX \longrightarrow AX + B$; where $A$ is more reactive than $B$.
In a double displacement reaction,two atoms or groups of atoms exchange their positions to form two new compounds.
$AB + CD \longrightarrow AD + CB$
Examples:
Displacement reaction:
$CuSO_{4(aq)} + Zn_{(s)} \longrightarrow ZnSO_{4(aq)} + Cu_{(s)}$
Double displacement reaction:
$Na_2SO_{4(aq)} + BaCl_{2(aq)} \longrightarrow BaSO_{4(s)} + 2NaCl_{(aq)}$