一、一些基本使用

1.1 toString

这个函数可以将一个数字转化为String类型，同时这个函数还有一个很重要的作用，将某个数字转化为特定进制下的表示

import java.util.*;public class test{public static void main(String[] args) throws InterruptedException {String baseChange=Integer.toString(7,2);System.out.println(baseChange);}}

输出：

一、属性

1.1 IntegerCache

/*** Cache to support the object identity semantics of autoboxing for values between* -128 and 127 (inclusive) as required by JLS.** The cache is initialized on first usage.  The size of the cache* may be controlled by the {@code -XX:AutoBoxCacheMax=<size>} option.* During VM initialization, java.lang.Integer.IntegerCache.high property* may be set and saved in the private system properties in the* sun.misc.VM class.*/private static class IntegerCache {static final int low = -128;static final int high;static final Integer cache[];static {// high value may be configured by propertyint 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);// Maximum array size is Integer.MAX_VALUEh = 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() {}}

二、方法

2.1 parseInt

/*** Parses the string argument as a signed decimal integer. The* characters in the string must all be decimal digits, except* that the first character may be an ASCII minus sign {@code '-'}* ({@code '\u005Cu002D'}) to indicate a negative value or an* ASCII plus sign {@code '+'} ({@code '\u005Cu002B'}) to* indicate a positive value. The resulting integer value is* returned, exactly as if the argument and the radix 10 were* given as arguments to the {@link #parseInt(java.lang.String,* int)} method.** @param s    a {@code String} containing the {@code int}*             representation to be parsed* @return     the integer value represented by the argument in decimal.* @exception  NumberFormatException  if the string does not contain a*               parsable integer.*/public static int parseInt(String s) throws NumberFormatException {return parseInt(s,10);}

/*** Parses the string argument as a signed integer in the radix* specified by the second argument. The characters in the string* must all be digits of the specified radix (as determined by* whether {@link java.lang.Character#digit(char, int)} returns a* nonnegative value), except that the first character may be an* ASCII minus sign {@code '-'} ({@code '\u005Cu002D'}) to* indicate a negative value or an ASCII plus sign {@code '+'}* ({@code '\u005Cu002B'}) to indicate a positive value. The* resulting integer value is returned.** <p>An exception of type {@code NumberFormatException} is* thrown if any of the following situations occurs:* <ul>* <li>The first argument is {@code null} or is a string of* length zero.** <li>The radix is either smaller than* {@link java.lang.Character#MIN_RADIX} or* larger than {@link java.lang.Character#MAX_RADIX}.** <li>Any character of the string is not a digit of the specified* radix, except that the first character may be a minus sign* {@code '-'} ({@code '\u005Cu002D'}) or plus sign* {@code '+'} ({@code '\u005Cu002B'}) provided that the* string is longer than length 1.** <li>The value represented by the string is not a value of type* {@code int}.* </ul>** <p>Examples:* <blockquote><pre>* parseInt("0", 10) returns 0* parseInt("473", 10) returns 473* parseInt("+42", 10) returns 42* parseInt("-0", 10) returns 0* parseInt("-FF", 16) returns -255* parseInt("1100110", 2) returns 102* parseInt("2147483647", 10) returns 2147483647* parseInt("-2147483648", 10) returns -2147483648* parseInt("2147483648", 10) throws a NumberFormatException* parseInt("99", 8) throws a NumberFormatException* parseInt("Kona", 10) throws a NumberFormatException* parseInt("Kona", 27) returns 411787* </pre></blockquote>** @param      s   the {@code String} containing the integer*                  representation to be parsed* @param      radix   the radix to be used while parsing {@code s}.* @return     the integer represented by the string argument in the*             specified radix.* @exception  NumberFormatException if the {@code String}*             does not contain a parsable {@code int}.*/public static int parseInt(String s, int radix)throws NumberFormatException{/** WARNING: This method may be invoked early during VM initialization* before IntegerCache is initialized. Care must be taken to not use* the valueOf method.*/if (s == null) {throw new NumberFormatException("null");}if (radix < Character.MIN_RADIX) {throw new NumberFormatException("radix " + radix +" less than Character.MIN_RADIX");}if (radix > Character.MAX_RADIX) {throw new NumberFormatException("radix " + radix +" greater than Character.MAX_RADIX");}int result = 0;boolean negative = false;int i = 0, len = s.length();int limit = -Integer.MAX_VALUE;int multmin;int digit;if (len > 0) {char firstChar = s.charAt(0);if (firstChar < '0') { // Possible leading "+" or "-"if (firstChar == '-') {negative = true;limit = Integer.MIN_VALUE;} else if (firstChar != '+')throw NumberFormatException.forInputString(s);if (len == 1) // Cannot have lone "+" or "-"throw NumberFormatException.forInputString(s);i++;}multmin = limit / radix;while (i < len) {// Accumulating negatively avoids surprises near MAX_VALUEdigit = 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;}

2.2 valueOf

/*** Returns an {@code Integer} object holding the* value of the specified {@code String}. The argument is* interpreted as representing a signed decimal integer, exactly* as if the argument were given to the {@link* #parseInt(java.lang.String)} method. The result is an* {@code Integer} object that represents the integer value* specified by the string.** <p>In other words, this method returns an {@code Integer}* object equal to the value of:** <blockquote>*  {@code new Integer(Integer.parseInt(s))}* </blockquote>** @param      s   the string to be parsed.* @return     an {@code Integer} object holding the value*             represented by the string argument.* @exception  NumberFormatException  if the string cannot be parsed*             as an integer.*/public static Integer valueOf(String s) throws NumberFormatException {return Integer.valueOf(parseInt(s, 10));}

/*** Returns an {@code Integer} object holding the value* extracted from the specified {@code String} when parsed* with the radix given by the second argument. The first argument* is interpreted as representing a signed integer in the radix* specified by the second argument, exactly as if the arguments* were given to the {@link #parseInt(java.lang.String, int)}* method. The result is an {@code Integer} object that* represents the integer value specified by the string.** <p>In other words, this method returns an {@code Integer}* object equal to the value of:** <blockquote>*  {@code new Integer(Integer.parseInt(s, radix))}* </blockquote>** @param      s   the string to be parsed.* @param      radix the radix to be used in interpreting {@code s}* @return     an {@code Integer} object holding the value*             represented by the string argument in the specified*             radix.* @exception NumberFormatException if the {@code String}*            does not contain a parsable {@code int}.*/public static Integer valueOf(String s, int radix) throws NumberFormatException {return Integer.valueOf(parseInt(s,radix));}

/*** Returns an {@code Integer} instance representing the specified* {@code int} value.  If a new {@code Integer} instance is not* required, this method should generally be used in preference to* the constructor {@link #Integer(int)}, as this method is likely* to yield significantly better space and time performance by* caching frequently requested values.** This method will always cache values in the range -128 to 127,* inclusive, and may cache other values outside of this range.** @param  i an {@code int} value.* @return an {@code Integer} instance representing {@code i}.* @since  1.5*/public static Integer valueOf(int i) {if (i >= IntegerCache.low && i <= IntegerCache.high)return IntegerCache.cache[i + (-IntegerCache.low)];return new Integer(i);}

jdk Integer 具体实现相关推荐

图解Java设计模式学习笔记——结构型模式(适配器模式、桥接模式、装饰者模式、组合模式、外观模式、享元模式、代理模式)
一.适配器模式(类适配器.对象适配器.接口适配器) 1.现实生活中的例子泰国插座用的是两孔的(欧标),可以买个多功能转换插头(适配器),这样就可以使用了国内的电器了. 2.基本介绍适配器模式(Ad ...
Java后端架构师的成长之路（二）——Java设计模式（2）
Java设计模式 23种设计模式结构型模式适配器模式基本介绍适配器模式工作原理类适配器模式对象适配器模式接口适配器模式适配器模式在SpringMVC框架应用的源码分析适配器模式的注意 ...
java int类源码,一起学JDK源码 -- Integer类
Integer类为java基本类型int的包装类,除了前面提到的Byte类,Short类中的大部分方法,Integer类中还提供了很多处理int类型的方法,接下来就让我们一起看看吧. 基础知识: 1. ...
JDK源码学习笔记——Integer
一.类定义 public final class Integer extends Number implements Comparable<Integer> 二.属性 private fi ...
java jdk缓存-128~127的Long与Integer
先推断下以下代码的输出结果 Qa:---------------------------------------------- Long a = Long.valueOf(127); ...
JDK源码解析 Integer类使用了享元模式
JDK源码解析 Integer类使用了享元模式. 我们先看下面的例子: public class Demo {public static void main(String[] args) {Integ ...
integer为null_走进 JDK 之 Integer
文中相关源码: Integer.java 开发的越久,越能体会到基础知识的重要性.抽空捋一下 JDK 源码,权当查漏补缺.读完之后,你会发现 JDK 源码真的会给你很多惊喜. Integer 是基本类 ...
JDK 源码 Integer解读之一（toString)
1:首先我们可以通过一个main函数,通过断点调试,正式开启Integer.toString()方法之旅. public static void main ( String[] arg ) { Sys ...
JDK源码分析-Integer
Integer是平时开发中最常用的类之一,但是如果没有研究过源码很多特性和坑可能就不知道,下面深入源码来分析一下Integer的设计和实现. Integer: 继承结构: -java.lang.Obj ...
JDK源码解析之 java.lang.Integer
teger 基本数据类型int 的包装类 Integer 类型的对象包含一个 int 类型的字段一.类定义 public final class Integer extends Number imp ...

jdk Integer 具体实现

一、一些基本使用

1.1 toString

一、属性

1.1 IntegerCache

二、方法

2.1 parseInt

2.2 valueOf

jdk Integer 具体实现相关推荐

最新文章

热门文章