像往常一样：没关系，但是如果您坚持花时间进行微优化，或者如果您真的想针对非常特殊的用例进行优化，请尝试以下操作：
import org.junit.Assert;import org.junit.Test;public class StringCharTest { // Times: // 1. Initialization of "s" outside the loop // 2. Init of "s" inside the loop // 3. newFunction() actually checks the string length, // so the function will not be optimized away by the hotstop compiler @Test // Fastest: 237ms / 562ms / 2434ms public void testCacheStrings() throws Exception { // Cache all possible Char strings String[] char2string = new String[Character.MAX_VALUE]; for (char i = Character.MIN_VALUE; i < Character.MAX_VALUE; i++) { char2string[i] = Character.toString(i); } for (int x = 0; x < 10000000; x++) { char[] s = "abcdefg".toCharArray(); for (int i = 0; i < s.length; i++) { newFunction(char2string[s[i]]); } } } @Test // Fast: 1687ms / 1725ms / 3382ms public void testCharToString() throws Exception { for (int x = 0; x < 10000000; x++) { String s = "abcdefg"; for (int i = 0; i < s.length(); i++) { // Fast: Creates new String objects, but does not copy an array newFunction(Character.toString(s.charAt(i))); } } } @Test // Very fast: 1331 ms/ 1414ms / 3190ms public void testSubstring() throws Exception { for (int x = 0; x < 10000000; x++) { String s = "abcdefg"; for (int i = 0; i < s.length(); i++) { // The fastest! Reuses the internal char array newFunction(s.substring(i, i + 1)); } } } @Test // Slowest: 2525ms / 2961ms / 4703ms public void testNewString() throws Exception { char[] value = new char[1]; for (int x = 0; x < 10000000; x++) { char[] s = "abcdefg".toCharArray(); for (int i = 0; i < s.length; i++) { value[0] = s[i]; // Slow! Copies the array newFunction(new String(value)); } } } private void newFunction(String string) { // Do something with the one-character string Assert.assertEquals(1, string.length()); }}
