完成String转换long的函数。

shengshijun · shengshijun · commit e26f9d7ece0e · 2015-02-27T18:02:28.000+08:00
StringBuilder实现longValue函数。
diff --git a/src/main/java/ssj/algorithm/math/MathUtil.java b/src/main/java/ssj/algorithm/math/MathUtil.java
@@ -248,6 +248,35 @@ public static int strToInt(String str) {
         return result;
     }
 
+    public static long strToLong(String str) {
+        Preconditions.checkNotNull(str);
+        Preconditions.checkArgument(str.length() > 0);
+        Preconditions.checkArgument(!(str.length() == 1 && (str.charAt(0) == '+' || str.charAt(0) == '-')));
+        long result = 0;
+        boolean is_negative = false;
+        int num_start = 0;
+        if (str.charAt(0) == '-') {
+            is_negative = true;
+            num_start = 1;
+        } else if (str.charAt(0) == '+') {
+            num_start = 1;
+        }
+
+        for (int i = num_start; i < str.length(); i++) {
+            long this_digit = str.charAt(i) - '0';
+            if (this_digit < 0 || this_digit > 9) {
+                throw new ArithmeticException("wrong format");
+            }
+            result = Math.multiplyExact(result, 10L);
+            if (is_negative) {
+                result = Math.subtractExact(result, this_digit);
+            } else {
+                result = Math.addExact(result, this_digit);
+            }
+        }
+        return result;
+    }
+
     public int closestBig(int origion) {
         Preconditions.checkArgument(origion > 0);
         int first_one_index = BitUtil.firstBitOne(origion);
diff --git a/src/main/java/ssj/algorithm/string/StringBuilder.java b/src/main/java/ssj/algorithm/string/StringBuilder.java
@@ -156,6 +156,10 @@ public int intValue() {
         return MathUtil.strToInt(toString());
     }
 
+    public long longValue() {
+        return MathUtil.strToLong(toString());
+    }
+
     public double doubleValue() {
         //TODO 完成String to double
         return -1;
