java字符串构造函数逻辑
我试图理解java字符串构造函数逻辑,java,string,Java,String,我试图理解java字符串是如何实现的。下面的jdk7源代码显示了对originalValue.length>大小的检查。我不知道它是如何实现的/何时实现的。我试着在一些java字符串创建语句上使用eclipse调试器,但是这个检查从来都不是真的。有可能设计一个字符串参数使这个检查成为真的吗 public final class String{ /** The value is used for character storage. */ private final char va
java字符串
是如何实现的。下面的jdk7源代码
显示了对originalValue.length>大小的检查。我不知道它是如何实现的/何时实现的。我试着在一些java字符串创建语句上使用eclipse调试器,但是这个检查从来都不是真的。有可能设计一个字符串参数使这个检查成为真的吗
public final class String{
/** The value is used for character storage. */
private final char value[];
/** The offset is the first index of the storage that is used. */
private final int offset;
/** The count is the number of characters in the String. */
private final int count;
/** Cache the hash code for the string */
private int hash; // Default to 0
/**
* 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.
*
* @param original
* A {@code String}
*/
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.copyOfRange(originalValue, off, off+size);
} else {
// The array representing the String is the same
// size as the String, so no point in making a copy.
v = originalValue;
}
this.offset = 0;
this.count = size;
this.value = v;
}
...
}
看看这段代码:
String s1 = "123456789";
String s2 = new String(s1.substring(0, 2));
第二个构造函数将匹配条件。诀窍在于子串方法。它不生成真正的子字符串,而是复制底层数组并为其设置新的边界。构造一个新字符串的想法是复制一个字符串,而不仅仅是分配相同的数组。这就是为什么从大字符串中提取小的子字符串可能导致OOM异常的原因。因为要表示一小段信息,需要使用大数组。您可以对此进行调试<代码>值
表示底层的char[]
<代码>计数表示视图
String s = new String("Hello "); //value= [H, e, l, l, o, , , ] count=8
String os = s.trim(); //value= [H, e, l, l, o, , , ] count=5
这里的s2.length>3吗?是的,因为它下面是相同的字符数组(不仅仅是相等的字符数组)。在这种情况下,s2的下划线数组的大小将是2,而不是9。