Integer a= 100,Ingeger b =100,Ingeter c=1000, Ingeter d=1000,system.out true,false

    技术2022-07-13  72

    面试题 public class Main { public static void main(String[] args) { Integer i1 = 100; Integer i2 = 100; Integer i3 = 200; Integer i4 = 200; System.out.println(i1==i2); System.out.println(i3==i4); } } 结果输出: true false

    原因: Integer i1 = 100; 实际上调用Integer i= Integer.valueOf(100)

    Integer源码:

    public static Integer valueOf(int i) { if (i >= IntegerCache.low && i <= IntegerCache.high) return IntegerCache.cache[i + (-IntegerCache.low)]; return new Integer(i); }

    如果不满足if条件就执行new Integer(i)

    public Integer (int value) { this value= value; }

    IntegerCache 是 Integer 的静态内部类,因此在 Integer 初始化时同时初始化 IntegerCache 及其所有属性

    private static class IntegerCache { static final int low = -128; // 缓存下界,值不可变 static final int high; // 缓存上界 static final Integer cache[]; // cache缓存是一个存放Integer类型的数组 static { // high value may be configured by property int h = 127; // getSavedProperty() 获取虚拟机启动时配置参数java.lang.Integer.IntegerCache.high的值, // 该值为自行设置的缓存上界,看下面代码 String integerCacheHighPropValue = sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high"); if (integerCacheHighPropValue != null) { try { int i = parseInt(integerCacheHighPropValue); i = Math.max(i, 127); // Maximum array size is Integer.MAX_VALUE h = Math.min(i, Integer.MAX_VALUE - (-low) -1); } catch( NumberFormatException nfe) { // If the property cannot be parsed into an int, ignore it. } } high = h; cache = new Integer[(high - low) + 1]; int j = low; for(int k = 0; k < cache.length; k++) cache[k] = new Integer(j++); // range [-128, 127] must be interned (JLS7 5.1.7) assert IntegerCache.high >= 127; } private IntegerCache() {} }
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