JDK之String的equals和equalsIgnoreCase的实现

    JDK8

    这俩个方法经常用，今天突然好奇怎么实现的，之前也看过，不过今天再来看下，记录下来

equalsIgnoreCase

    List-1

1public boolean equalsIgnoreCase(String anotherString) {
2    return (this == anotherString) ? true
3            : (anotherString != null)
4            && (anotherString.value.length == value.length)
5            && regionMatches(true, 0, anotherString, 0, value.length);
6}
7
8...
9public boolean regionMatches(boolean ignoreCase, int toffset,
10                             String other, int ooffset, int len) {
11    char ta[] = value;
12    int to = toffset;
13    char pa[] = other.value;
14    int po = ooffset;
15    // Note: toffset, ooffset, or len might be near -1>>>1.
16    if ((ooffset < 0) || (toffset < 0)
17            || (toffset > (long)value.length - len)
18            || (ooffset > (long)other.value.length - len)) {
19        return false;
20    }
21    while (len-- > 0) {
22        char c1 = ta[to++];
23        char c2 = pa[po++];
24        if (c1 == c2) {
25            continue;
26        }
27        if (ignoreCase) {
28            // If characters don't match but case may be ignored,
29            // try converting both characters to uppercase.
30            // If the results match, then the comparison scan should
31            // continue.
32            char u1 = Character.toUpperCase(c1);
33            char u2 = Character.toUpperCase(c2);
34            if (u1 == u2) {
35                continue;
36            }
37            // Unfortunately, conversion to uppercase does not work properly
38            // for the Georgian alphabet, which has strange rules about case
39            // conversion.  So we need to make one last check before
40            // exiting.
41            if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
42                continue;
43            }
44        }
45        return false;
46    }
47    return true;
48}

    如List-1所示:

•     判断是否是本身
•     判断不为空，判断长度是否相等
•     在regionMatches方法中，俩个char[]从左边开始往右边逐个对比，如果直接比较俩个字符，不相等的话，将俩个字符先都转换为大写进行比较，如果大写不相等，那么再转换为小写——注释上写着格鲁吉亚的字符有问题

equals

    List-2

1public boolean equals(Object anObject) {
2    if (this == anObject) {
3        return true;
4    }
5    if (anObject instanceof String) {
6        String anotherString = (String)anObject;
7        int n = value.length;
8        if (n == anotherString.value.length) {
9            char v1[] = value;
10            char v2[] = anotherString.value;
11            int i = 0;
12            while (n-- != 0) {
13                if (v1[i] != v2[i])
14                    return false;
15                i++;
16            }
17            return true;
18        }
19    }
20    return false;
21}

•     判断是否是本身
•     判断长度，如果长度一样，那么逐个字符的比较