用于Bigdecimal null验证的三元运算符

Question

Why am I getting null pointer exception in this code?

    BigDecimal test = null;
    String data = "";
    try {
    System.out.println(test==null?"":test.toString());
    data = test==null?"":test.toString();
    System.out.println(data);
    data = data +  " " + test==null?"":test.toString(); // catching null pointer in this line
    } catch (Exception e) {
        // TODO: handle exception
        e.printStackTrace();
    }

Answer 1

It's evaluating the expressions as:

data = (data +  " " + test==null)?"":test.toString();

so, since data + " " + test is not null , it attempts to call test.toString() even when test is null .

Change

data = data +  " " + test==null?"":test.toString();

to

data = data +  " " + (test==null?"":test.toString());

Answer 2

Since Java 8 there is also an alternative way to deal with potential null references: Optional

To prevent an NPE while converting a BigDecimal to a String you can use an Optional like that:

String data = Optional.ofNullable(test).map(BigDecimal::toString).orElse("");

This way you don't need to check test several times if it is null . Having test once wrapped in an Optional you could work on being safe, that any conversion ( map ) will be performed only if test is not referencing null .