原始类型包装类解读（Float、Double）

Double和Float包含的方法大致一样，所以这里重点看Float，Double可以参照Float。

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Float继承自Number，仅有一个final float类型的成员变量value，用来保存对应的原始类型。

静态常量

//正无穷大，ps：谁说0不能做除数的
public static final float POSITIVE_INFINITY = 1.0f / 0.0f;
//负无穷大
public static final float NEGATIVE_INFINITY = -1.0f / 0.0f;
//NaN(Not a Number)
public static final float NaN = 0.0f / 0.0f;
public static final float MAX_VALUE = 0x1.fffffeP+127f;
public static final float MIN_NORMAL = 0x1.0p-126f;
public static final float MIN_VALUE = 0x0.000002P-126f;
//占用32bit
public static final int SIZE = 32;
public static final int BYTES = SIZE / Byte.SIZE;
public static final Class TYPE = (Class) float[].class.getComponentType();

构造函数

    public Float(float value) {
        this.value = value;
    }

    public Float(double value) {
        this.value = (float)value;
    }

    public Float(String s) throws NumberFormatException {
        value = parseFloat(s);
    }

public static native float intBitsToFloat(int bits)

将整型参数对应的32位bit值转换为对应的浮点数。
如：

• 0x7f800000对应POSITIVE_INFINITY
• 0xff800000对应NEGATIVE_INFINITY
• 0x7fc00000对应NaN
• 0x7f7fffff对应MAX_VALUE
• 0x1对应MIN_VALUE

其他方法

    public boolean isNaN() {
        return isNaN(value);
    }

    public boolean isInfinite() {
        return isInfinite(value);
    }

    public static boolean isNaN(float v) {
        return (v != v);
    }

    public static boolean isInfinite(float v) {
        return (v == POSITIVE_INFINITY) || (v == NEGATIVE_INFINITY);
    }

    public static Float valueOf(float f) {
        return new Float(f);
    }

    public static Float valueOf(String s) throws NumberFormatException {
        return new Float(parseFloat(s));
    }

    public static float parseFloat(String s) throws NumberFormatException {
        return FloatingDecimal.parseFloat(s);
    }

    //是否是有限的
    public static boolean isFinite(float f) {
       return Math.abs(f) <= FloatConsts.MAX_VALUE;
    }

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Double

静态常量

public static final double POSITIVE_INFINITY = 1.0 / 0.0;
public static final double NEGATIVE_INFINITY = -1.0 / 0.0;
public static final double NaN = 0.0d / 0.0;
public static final double MAX_VALUE = 0x1.fffffffffffffP+1023;
public static final double MIN_NORMAL = 0x1.0p-1022;
public static final double MIN_VALUE = 0x0.0000000000001P-1022;
public static final int SIZE = 64;
public static final int BYTES = SIZE / Byte.SIZE;
public static final Class TYPE = (Class) double[].class.getComponentType();