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10 Integer：深入剖析最常用的整数包装类
时间：2026-06-01 15:40:01 编辑：袖梨 来源：一聚教程网
Integer作为Java最基础的包装类，其设计精妙与性能优化值得开发者深入探究。本文将全面剖析其核心机制与实战应用场景。
Integer —— 最常用的整数包装类深度解析
一、Integer 的类结构
public final class Integer extends Number implements Comparable { @Native public static final int MIN_VALUE = 0x80000000; // -2^31
@Native public static final int MAX_VALUE = 0x7fffffff; // 2^31 - 1 public static final Class TYPE
= (Class) Class.getPrimitiveClass("int"); public static final int SIZE = 32;
public static final int BYTES = SIZE / Byte.SIZE; private final int value; private static final long serialVersionUID = 1360826667806852920L;
}
二、IntegerCache —— 面试必问的缓存机制
private static class IntegerCache {
static final int low = -128;
static final int high;
static final Integer cache[]; static {
int h = 127;
String integerCacheHighPropValue =
sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
if (integerCacheHighPropValue != null) {
try {
int i = parseInt(integerCacheHighPropValue);
i = Math.max(i, 127);
// 防止缓存数组过大
h = Math.min(i, Integer.MAX_VALUE - (-low) - 1);
} catch (NumberFormatException nfe) {
// 配置错误则忽略
}
}
high = h;
cache = new Integer[(high - low) + 1];
int j = low;
for (int k = 0; k < cache.length; k++) {
cache[k] = new Integer(j++);
}
} private IntegerCache() {}
}
缓存生效场景
public class IntegerCacheDemo {
public static void main(String[] args) {
Integer a = 127;
Integer b = 127;
System.out.println(a == b); // true——都是缓存中同一对象 Integer c = 128;
Integer d = 128;
System.out.println(c == d); // false——超出缓存范围，各自 new // 显式调用 valueOf 同样走缓存
System.out.println(Integer.valueOf(100) == Integer.valueOf(100)); // true // new Integer 始终不走缓存
System.out.println(new Integer(100) == new Integer(100)); // false
}
}
调整缓存上限
# 设置缓存上限为 1000
java -Djava.lang.Integer.IntegerCache.high=1000 MyApp
三、自动装箱与拆箱
public class BoxingDemo {
public static void main(String[] args) {
Integer boxed = 42; // 等价于 Integer.valueOf(42) int unboxed = boxed; // 等价于 boxed.intValue() Integer x = 100, y = 200;
Integer z = x + y; // 拆箱 → 计算 → 装箱 Integer n1 = null;
// 下面这行会抛出 NullPointerException（n1 拆箱为 int 时）
// int result = true ? n1 : 0;
} // 实际编译后的字节码等价于：
// Integer boxed = Integer.valueOf(42);
// int unboxed = boxed.intValue();
}
四、进制转换方法
4.1 toString(int i, int radix)
public static String toString(int i, int radix) {
if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
radix = 10;
if (radix == 10) return toString(i);
char buf[] = new char[33];
boolean negative = (i < 0);
int charPos = 32;
if (!negative) i = -i;
while (i <= -radix) {
buf[charPos--] = digits[-(i % radix)];
i = i / radix;
}
buf[charPos] = digits[-i];
if (negative) buf[--charPos] = '-';
return new String(buf, charPos, (33 - charPos));
}
public class RadixDemo {
public static void main(String[] args) {
int val = 255;
System.out.println("十进制: " + Integer.toString(val, 10)); // 255
System.out.println("二进制: " + Integer.toString(val, 2)); // 11111111
System.out.println("八进制: " + Integer.toString(val, 8)); // 377
System.out.println("十六进制: " + Integer.toString(val, 16)); // ff
System.out.println("三十二进制: " + Integer.toString(val, 32)); // 7v
}
}
4.2 toHexString / toOctalString / toBinaryString
public static String toHexString(int i) {
return toUnsignedString0(i, 4); // 4位一组 → 十六进制
}public static String toOctalString(int i) {
return toUnsignedString0(i, 3); // 3位一组 → 八进制
}public static String toBinaryString(int i) {
return toUnsignedString0(i, 1); // 1位一组 → 二进制
}
五、parseInt —— 字符串解析精要
public static int parseInt(String s, int radix) throws NumberFormatException {
if (s == null) throw new NumberFormatException("null");
if (radix < Character.MIN_RADIX)
throw new NumberFormatException("radix " + radix + " less...");
if (radix > Character.MAX_RADIX)
throw new NumberFormatException("radix " + radix + " greater..."); int result = 0;
boolean negative = false;
int i = 0, len = s.length();
int limit = -Integer.MAX_VALUE; if (len > 0) {
char firstChar = s.charAt(0);
if (firstChar < '0') {
if (firstChar == '-') { negative = true; limit = Integer.MIN_VALUE; }
else if (firstChar != '+') throw NumberFormatException.forInputString(s);
if (len == 1) throw NumberFormatException.forInputString(s);
i++;
}
int multmin = limit / radix;
while (i < len) {
int digit = Character.digit(s.charAt(i++), radix);
if (digit < 0) throw NumberFormatException.forInputString(s);
if (result < multmin) throw NumberFormatException.forInputString(s);
result *= radix;
if (result < limit + digit) throw NumberFormatException.forInputString(s);
result -= digit;
}
} else {
throw NumberFormatException.forInputString(s);
}
return negative ? result : -result;
}
设计亮点：使用负累加而非正累加，避免 Integer.MIN_VALUE 取负时的溢出问题。
六、位运算方法
6.1 highestOneBit / lowestOneBit
public static int highestOneBit(int i) {
i |= (i >> 1);
i |= (i >> 2);
i |= (i >> 4);
i |= (i >> 8);
i |= (i >> 16);
return i - (i >>> 1);
}public static int lowestOneBit(int i) {
return i & -i; // 利用补码特性
}
public class BitDemo {
public static void main(String[] args) {
int val = 18; // 二进制: 00010010 System.out.println("highestOneBit(18): " + Integer.highestOneBit(val)); // 16
System.out.println("lowestOneBit(18): " + Integer.lowestOneBit(val)); // 2 // highestOneBit 的应用：快速找到 <= n 的最大2的幂
System.out.println("2^{log2(100)}: " + Integer.highestOneBit(100)); // 64
}
}
6.2 bitCount —— 统计 1 的个数
public static int bitCount(int i) {
i = i - ((i >>> 1) & 0x55555555);
i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
i = (i + (i >>> 4)) & 0x0f0f0f0f;
i = i + (i >>> 8);
i = i + (i >>> 16);
return i & 0x3f;
}
6.3 numberOfLeadingZeros / numberOfTrailingZeros
public static int numberOfLeadingZeros(int i) {
if (i == 0) return 32;
int n = 1;
if (i >>> 16 == 0) { n += 16; i <<= 16; }
if (i >>> 24 == 0) { n += 8; i <<= 8; }
if (i >>> 28 == 0) { n += 4; i <<= 4; }
if (i >>> 30 == 0) { n += 2; i <<= 2; }
n -= i >>> 31;
return n;
}
七、decode —— 多进制解码器
public static Integer decode(String nm) throws NumberFormatException
解码规则：
| 前缀 | 进制 | 示例 |
|---|---|---|
0x / 0X | 十六进制 | 0xFF → 255 |
# | 十六进制 | #FF → 255 |
0 | 八进制 | 0377 → 255 |
| 无前缀 | 十进制 | 255 → 255 |
public class DecodeDemo {
public static void main(String[] args) {
System.out.println(Integer.decode("255")); // 255
System.out.println(Integer.decode("0xFF")); // 255
System.out.println(Integer.decode("0XFF")); // 255
System.out.println(Integer.decode("#FF")); // 255
System.out.println(Integer.decode("-0xFF")); // -255
System.out.println(Integer.decode("0377"));
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