String中的subString方法的内存泄露问题.docVIP

String中的subString方法的内存泄露问题 What’s the problem? String的subString()会产生内存泄露。 What’s the root cause? subString的源码： public String substring(int beginIndex, int endIndex) { if (beginIndex 0) { throw new StringIndexOutOfBoundsException(beginIndex); } if (endIndex count) { throw new StringIndexOutOfBoundsException(endIndex); } if (beginIndex endIndex) { throw new StringIndexOutOfBoundsException(endIndex - beginIndex); } return ((beginIndex == 0) (endIndex == count)) ? this : new String(offset + beginIndex, endIndex - beginIndex, value); } 问题就在最后一句：new String(offset + beginIndex, endIndex - beginIndex, value) 从String的构造函数源码看： // Package private constructor which shares value array for speed. String(int offset, int count, char value[]) { this.value = value; //还是原值 this.offset = offset; this.count = count; } 从这里看出，subString并不是构造一个新的String对象，而是重用了原先对象的char[]，通过修改了初始偏移量和有效字符数来达到重用的目的。（这样的好处是可以避免内存拷贝，加快速度） 但是其实subString出来的子对象，仍然是原对象的一个引用。 private void testString() { String A = new String(hello, world); String B = a.substring(2，4); } 如图： 此时，当A不再使用的，由于B仍然指向了该内存空间，导致h等红色空间并不能被系统马上回收；当B长期被占用，并且被引用多次的时候，内存空间就回收的越慢。 (3) What’s the solution? 使用String的构造函数String(String original) /**?Initializes?a?newly?created?{@code?String}?object?so?that?it represents?the?same?sequence?of?characters?as?the?argument;?in?other?words,?the?newly?created?string?is?a?copy?of?the?argument?string.?Unless?an?explicit?copy?of?{@code?original}?is?needed,?use?of?this?constructor?is?unnecessary?since?Strings?are?immutable.? */?? public?String(String?original) {?? int?size?=?original.count;?? ? char[]?originalValue?=?original.value;?? ??char[]?v;?? if?(originalValue.length??size) {?? ?????//?The?array?representing?the?String?is?bigger?than?the?new?? ?? //?String?itself.??Perhaps?this?constructor?is?being?called?? ???? //?in?order?to?trim?the?baggage,?so?make?a?copy?of?the?array.????????int?off?=?original.offset;?? ?????v?=?Arrays.copyOf