String源碼里的這兩個方法如下:
public boolean regionMatches(int toffset, String other, int ooffset,
int len) {
char ta[] = value;
int to = toffset;
char pa[] = other.value;
int po = ooffset;
// Note: toffset, ooffset, or len might be near -1>>>1.
if ((ooffset < 0) || (toffset < 0)
|| (toffset > (long)value.length - len)
|| (ooffset > (long)other.value.length - len)) {
return false;
}
while (len-- > 0) {
if (ta[to++] != pa[po++]) {
return false;
}
}
return true;
}
public boolean regionMatches(boolean ignoreCase, int toffset,
String other, int ooffset, int len) {
char ta[] = value;
int to = toffset;
char pa[] = other.value;
int po = ooffset;
// Note: toffset, ooffset, or len might be near -1>>>1.
if ((ooffset < 0) || (toffset < 0)
|| (toffset > (long)value.length - len)
|| (ooffset > (long)other.value.length - len)) {
return false;
}
while (len-- > 0) {
char c1 = ta[to++];
char c2 = pa[po++];
if (c1 == c2) {
continue;
}
if (ignoreCase) {
// If characters don't match but case may be ignored,
// try converting both characters to uppercase.
// If the results match, then the comparison scan should
// continue.
char u1 = Character.toUpperCase(c1);
char u2 = Character.toUpperCase(c2);
if (u1 == u2) {
continue;
}
// Unfortunately, conversion to uppercase does not work properly
// for the Georgian alphabet, which has strange rules about case
// conversion. So we need to make one last check before
// exiting.
if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
continue;
}
}
return false;
}
return true;
}
但是，明顯可以這么寫
public boolean regionMatches(int toffset, String other, int ooffset,int len) {
return regionMatches(false,toffset, other, ooffset, len);
}
但是jdk8里還是這樣分開實現的，是處于什么其他考慮嗎？ (話說string里類似的重復實現還有不少)
1 回答
慕少森
TA貢獻2019條經驗 獲得超9個贊
測試程序：
String s1 = "oshagoeutno;shfsSFSDAFsfjgpdhsf;AJofdi1248938jdsgjJDJFSDoghp79874hgajfJDy9(FS*U9prhgdsjfdghnsdfasf";
String s2 = "oshagoeutno;shfsSFSDAFsfjgpdhsf;AJofdi1248938jfogheyjJDJFSDoghp79874hgajfJDy9(FS*U9prhgdsjfdghnsdfasf";
long start = System.nanoTime();
for (int i = 0; i < 10_000_000; i++) {
s1.regionMatches(5, s2, 5, 65);
}
long end = System.nanoTime();
System.out.println("regionMatches(): " + (end - start));
start = System.nanoTime();
for (int i = 0; i < 10_000_000; i++) {
s1.regionMatches(false, 5, s2, 5, 65);
}
end = System.nanoTime();
System.out.println("regionMatches(false): " + (end - start));結果：
regionMatches(): 633992574
regionMatches(false): 805662114第一個比第二個稍微快一些。
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