Make String.format(“%s”, arg) display null-valued arguments differently from “null”

Question

Consider the custom toString() implementation of a bean:

@Override
public String toString() {
    String.format(\"this is %s\", this.someField);
}
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Answer 1

From java 7, you can use Objects.toString(Object o, String nullDefault).

Applied to your example: String.format("this is %s", Objects.toString(this.someField, "?"));

Answer 2

A bit late on the subject, but this could be a quite clean-looking solution : First, create your own format method...

private static String NULL_STRING = "?";

private static String formatNull(String str, Object... args){
    for(int i = 0; i < args.length; i++){
        if(args[i] == null){
            args[i] = NULL_STRING;
        }
    }

    return String.format(str, args);
}

Then, use it as will...

@Test
public void TestNullFormat(){
    Object ob1 = null;
    Object ob2 = "a test";

    String str = formatNull("this is %s", ob1);
    assertEquals("this is ?", str);

    str = formatNull("this is %s", ob2);
    assertEquals("this is a test", str);
}

This eliminates the need for multiple, hard-to-read, ternary operators.

Answer 3

If you don't want to use replaceAll(), You can assign a default text(String) for someField.

But if some time this may assign null again. So you can use validation for that case

 this.someField == null ? "defaultText" : this.someField

Answer 4

public static String format(String format, Object... args){
    for (int i=0;i<args.length;i++){
        if (args[i]==null) args[i]="";
    }
    return String.format(format,args);
}

then use the method ，ok