java中封装类共九个,分别是Boolean,Byte,Short,Integer,Long,Float,Double,Character,Void
其中Void对于使用者并无多大意义,也不可以构造任何对象,代码如下:
package java.lang; public final class Void { public static final Class<Void> TYPE = Class.getPrimitiveClass("void"); private Void() {} }
这几个封装类中,以Boolean类型最简单,Character最复杂,Character个人觉得也是整个java中最复杂的一个类,先说Boolean:
package java.lang; public final class Boolean implements java.io.Serializable,Comparable<Boolean>{ public static final Boolean TRUE = new Boolean(true); public static final Boolean FALSE = new Boolean(false); public static final Class<Boolean> TYPE = Class.getPrimitiveClass("boolean"); private final boolean value; private static final long serialVersionUID = -3665804199014368530L; public Boolean(boolean value) { this.value = value; } public Boolean(String s) { this(toBoolean(s)); } public static boolean parseBoolean(String s) { return toBoolean(s); } public boolean booleanValue() { return value; } public static Boolean valueOf(boolean b) { return (b ? TRUE : FALSE); } public static Boolean valueOf(String s) { return toBoolean(s) ? TRUE : FALSE; } public static String toString(boolean b) { return b ? "true" : "false"; } public String toString() { return value ? "true" : "false"; } public int hashCode() { return value ? 1231 : 1237; } public boolean equals(Object obj) { if (obj instanceof Boolean) { return value == ((Boolean)obj).booleanValue(); } return false; } public static boolean getBoolean(String name) { boolean result = false; try { result = toBoolean(System.getProperty(name)); } catch (IllegalArgumentException e) { } catch (NullPointerException e) { } return result; } public int compareTo(Boolean b) { return compare(this.value, b.value); } public static int compare(boolean x, boolean y) { return (x == y) ? 0 : (x ? 1 : -1); } private static boolean toBoolean(String name) { return ((name != null) && name.equalsIgnoreCase("true")); } }
Boolean实现了Comparable接口,也就是说boolean类型本身是可以比较的,而对于boolean类型而言,在java中认为true是大于false的。示例如下:
package demo.nio; public class BooleanDemo { public static void main(String[] args){ System.out.println(Boolean.compare(true, false));//1 代表大于 System.out.println(Boolean.compare(false, false));//0 代表等于 System.out.println(Boolean.compare(true, true));//0 代表等于 System.out.println(Boolean.compare(false, true));//-1 代表小于 } }
值得一提的是Boolean的hashcode是两个常数,这就保证了不管从何处new的对象,只要内部的value字段值为true,它的hashcode就是1231,为false就是1237。equals方法完全调用了内部value字段的==操作。所有的封装类型都包含了valueOf的静态函数,并且有
两个重载版本,分别是基元类型参数和字符串参数。还有一个parse函数,内部可以通过返回Cache中的数据来避免重复的装箱操作。java中对于Boolean的Cache就是 Boolean.TRUE和Boolean.FALSE两个静态字段。它们是公共类型。
public class BooleanDemo { public static void main(String[] args){ Boolean b3 = Boolean.valueOf(true); Boolean b4 = Boolean.valueOf("true"); Boolean b5 = Boolean.parseBoolean("true"); } }
时间: 2024-10-06 08:14:35