JAVA源码String学习

String 内部是用char数组存储数据，主要就是对这三个属性进行操作。

 /** 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;

indexOf函数

import java.util.HashMap;import java.util.Map;public class App {public static void main(String[] args) {String str = new String("dddasdadad");char[] strChar = str.toCharArray();String str1 = new String("ad");char[] str1Char = str1.toCharArray();                int result = indexOf(strChar, 0, 9, str1Char, 0, 2, 0);                System.out.println(result);}static int indexOf(char[] source, int sourceOffset, int sourceCount,char[] target, int targetOffset, int targetCount, int fromIndex) {if (fromIndex >= sourceCount) {return (targetCount == 0 ? sourceCount : -1);}if (fromIndex < 0) {fromIndex = 0;}if (targetCount == 0) {return fromIndex;}char first = target[targetOffset];int max = sourceOffset + (sourceCount - targetCount);for (int i = sourceOffset + fromIndex; i <= max; i++) {/*找到目标数组的第一个字符在原字符数组中第一次出现的位置 */if (source[i] != first) {while (++i <= max && source[i] != first) ; //此处写法可学习}/* 通过上面的while循环找到第一次出现的位置后，循环对比目标数组剩下的字符是否和原字符数组相对位置的相同 */if (i <= max) {int j = i + 1; //4int end = j + targetCount - 1; //5for (int k = targetOffset + 1; j < end && source[j] == target[k]; j++, k++);  //此处写法可学习if (j == end) {/* 因为上面会j++,所以若相同则找到全部字符数组,返回第一次出现的位置i. */return i - sourceOffset;}}}return -1;}}

lastIndexOf函数

public class App {public static void main(String[] args) {String str = new String("dddasdadad");          char[] strChar = str.toCharArray();        String str1 = new String("da");        char[] str1Char = str1.toCharArray();System.out.println(lastIndexOf(strChar, 0, 10, str1Char, 0, 2,5));}static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,char[] target, int targetOffset, int targetCount, int fromIndex) {/* * Check arguments; return immediately where possible. For consistency, * don't check for null str. */int rightIndex = sourceCount - targetCount; if (fromIndex < 0) { return -1;}if (fromIndex > rightIndex) {fromIndex = rightIndex; }/* 空字符串也匹配 */if (targetCount == 0) {return fromIndex;}/* 目标数组最后一个元素在数组的位置 */int strLastIndex = targetOffset + targetCount - 1;/*  目标数组最后一个元素*/char strLastChar = target[strLastIndex];/*  原数组最后一个需要校验的位置*/int min = sourceOffset + targetCount - 1;/*  原数组开始校验的位置*/int i = min + fromIndex;startSearchForLastChar: while (true) {  /*此处可学习*//* 从原数组最后一位数找到目标数组最后一位第一次出现的位置 i */while (i >= min && source[i] != strLastChar) {i--;}if (i < min) {return -1;}int j = i - 1;int start = j - (targetCount - 1);int k = strLastIndex - 1;/* 原数组和目标数组剩下的位置字符一一对比,若不相同则将i-1跳至上面继续执行 */while (j > start) {if (source[j--] != target[k--]) {i--;continue startSearchForLastChar;}}return start - sourceOffset + 1;}}}