What's wrong with new String?

Question

I just failed a code review without any reason given due to my writing, for a function where s (of type String) is passed as a parameter

if (s == null){
    s = new String();
}

Said I should use s = ""; instead. Why?

Answer 1

You could always clarify with the reviewer?

new String(); always creates a new string. (Isn't the Java syntax self-explantory?)

s = "" ; will set the reference to an interned string and is therefore preferred.

Answer 2

当使用文字进行初始化时， String StringPool使用new关键字进行初始化具有优先级，这是因为JVM优化了，并且因为JVM直接在StringPool分配了使用文字进行初始化的StringPool 。

Answer 3

Both s = new String();s = ""; expressions give a string object but there is a clear difference between the two. s=new String() will create a new object in the heap memory whereas if we create object using string literal s = ""; it may return an existing object from String pool( a cache of string objects ) if it already exists.

Example will make it more clear:

String a= "banana";
String b= "banana";

Here both a and b refer to the same object and hence a==b is true

String a =new String("banana")
String b= new String("banana")

Here both a and b refer to two different objects and hence a==b is false

Answer 4

JVM handle it differently if you call:

• s = new String(); //The constructor will create new object everytime it's called
• s = ""; //The string literal will refer to the same object in the common pool

You can find the full answer in the link bebow: http://o7planning.org/web/fe/default/en/document/19529/string-stringbuffer-and-stringbuilder-tutorial

Example:

public static void main(String[] args) {
    String str1 = "apple";
    String str2 = "apple";

    if(str1 == str2) {
        System.out.println("str1, str2: same object");
    } else {
        System.out.println("str1, str2: different object");
    }

    String str3 = new String("apple");
    String str4 = new String("apple");

    if(str3 == str4) {
        System.out.println("str3, str4: same object");
    } else {
        System.out.println("str3, str4: different object");
    }       
}