Different implementations of string.substring in Android and Java

Lucky to go to Sogou today, there is a very interesting question

String str1 = "test for Sougou"; String str2 = str1.substring (5);

Test Center is whether STR2 generates a new character array to save "for Sougou"

At that time I thought string inside was encapsulated a char[], cannot be like CPP as the first address plus a number to do char[] reuse

The new string must be arraycopy once to implement the SUBSTRING function, so there must be new memory generation

Came back to see the realization of

Because Android Studio was on, it looked under Android under the String.substring implementation, and sent to the classmate

Public String substring (int start) {        if (start = = 0) {            return this;        }        If (Start >= 0 && start <= count) {            return new String (offset + start, count-start, value);        }        Throw Indexandlength (start);    }

String (int offset, int charcount, char[] chars) {        this.value = chars;        This.offset = offset;        This.count = charcount;    }

Use the member variable offset to save the next offset, directly to the char[] reference to the new string, no memory requested

Sigh good subtle realization at the same time, find yourself doing wrong

Who knows the classmate read the source code after asked me what version of the JDK, and his side of the implementation is not the same

Public String substring (int beginindex) {        if (Beginindex < 0) {            throw new stringindexoutofboundsexception ( beginindex);        }        int sublen = Value.length-beginindex;        if (Sublen < 0) {            throw new stringindexoutofboundsexception (Sublen);        }        return (Beginindex = = 0)? This:new String (value, Beginindex, Sublen);    }

Public String (char value[], int offset, int count) {        if (offset < 0) {            throw new Stringindexoutofboundsexceptio n (offset);        }        if (Count < 0) {            throw new stringindexoutofboundsexception (count);        }        Note:offset or count might be near-1>>>1.        if (Offset > Value.length-count) {            throw new Stringindexoutofboundsexception (offset + count);        }        This.value = Arrays.copyofrange (value, offset, offset+count);    }

In addition to Beginindex=0 is directly returned to the current outside, all others are arraycopy

Yes!!! New memory in JDK!!!
It must be said that Google programmers are really

Different implementations of string.substring in Android and Java