Does Java support default parameter values?

Question

I came across some Java code that had the following structure:

public MyParameterizedFunction(String param1, int param2)
{
    this(param1, param2, false);
}         


        

Answer 1

Unfortunately, yes.

void MyParameterizedFunction(String param1, int param2, bool param3=false) {}

could be written in Java 1.5 as:

void MyParameterizedFunction(String param1, int param2, Boolean... params) {
    assert params.length <= 1;
    bool param3 = params.length > 0 ? params[0].booleanValue() : false;
}

But whether or not you should depend on how you feel about the compiler generating a

new Boolean[]{}

for each call.

For multiple defaultable parameters:

void MyParameterizedFunction(String param1, int param2, bool param3=false, int param4=42) {}

could be written in Java 1.5 as:

void MyParameterizedFunction(String param1, int param2, Object... p) {
    int l = p.length;
    assert l <= 2;
    assert l < 1 || Boolean.class.isInstance(p[0]);
    assert l < 2 || Integer.class.isInstance(p[1]);
    bool param3 = l > 0 && p[0] != null ? ((Boolean)p[0]).booleanValue() : false;
    int param4 = l > 1 && p[1] != null ? ((Integer)p[1]).intValue() : 42;
}

This matches C++ syntax, which only allows defaulted parameters at the end of the parameter list.

Beyond syntax, there is a difference where this has run time type checking for passed defaultable parameters and C++ type checks them during compile.