0. 几点说明

本博客主要研究不同类型数据之间相互转换以及常见的操作，StringBuilder和StringBuffer主要差别在于前者非线程安全，后者线程安全，方法差别不大，因此下文只研究了StringBuilder的相关操作。

为了更加深入的理解实现过程中相关变量的类型，建议使用getClass方法查看

ArrayList类型打印结果是以 “[ ]” 包围的  

数组直接打印的不会出现数组中的元素，只会出现数组变量在堆中的地址。可以使用Arrays.toString()查看数组。

数组，ArrayList，Set都可以使用foreach依次获取数据。

1. String，StringBuilder，数组，列表声明

1.1 声明数组

//注意数组必须要声明大小，如果无法确定，需要使用列表

String[] aArray = new String[5];

String[] bArray = {"a", "b", "c", "d", "e"};

String[] cArray = new String[]{"a", "b", "c", "d", "e"};

1.2 声明一个String变量

String str = "hello world";

1.3 声明一个StringBuilder(StringBuffer)变量

StringBuilder sb1 = new StringBuilder();// 构造一个空的字符串缓冲区，并且初始化为 16 个字符的容量。

StringBuilder sb2 = new StringBuilder(10);// 创建一个空的字符串缓冲区，并且初始化为指定长度 length 的容量。

StringBuilder sb3 = new StringBuilder("hello world");// 创建一个字符串缓冲区，并将其内容初始化为指定的字符串内容str,字符串缓冲区的初始容量为 16 加上字符串str的长度。

System.out.println("sb3: " + sb3.append(" java"));// sb3: hello world java

1.4 声明一个ArrayList变量

ArrayList<String> arrList = new ArrayList<String>();

arrList.add("hello ");

arrList.add("world");

System.out.println("arrList: " + arrList);// arrList: [hello , world]

2. char，String，StringBuilder，数组，列表之间相互转换

2.1 数组 to ArrayList

ArrayList<String> arrList1 = new ArrayList<String>(Arrays.asList(cArray));

System.out.println("arrList1: " + arrList1);// arrList1: [a, b, c, d, e]

2.2 ArrayList to 数组

String[] dArray = new String[arrList1.size()];

arrList1.toArray(dArray);

System.out.println("dArray: " + Arrays.toString(dArray));// dArray: [a, b, c, d, e]

2.3 String to StringBuilder

String str1 = "hello ";

String str2 = "world";

StringBuilder sb4 = new StringBuilder();

sb4.append(str1).append(str2);

System.out.println("sb4: " + sb4);// sb4: hello world

2.4 StringBuilder to String

System.out.println("sb4:" + sb4.toString());// sb4:hello world

System.out.println("sb4.class: " + sb4.toString().getClass());// sb4.class: class java.lang.String

2.5 String to ArrayList

ArrayList<String> arrList2 = new ArrayList<String>();

//arrList2.add(str).add(str1); 错误

arrList2.add(str);

arrList2.add(str1);

arrList2.add(str2);

System.out.println("arrList2: " + arrList2);// arrList2: [hello world, hello , world]

2.6 ArrayList to String

String[] eArray = new String[arrList2.size()];

System.out.println("eArray: " + Arrays.toString(arrList2.toArray(eArray)));// eArray: [hello world, hello , world]

2.7 String to String[]

String[] fArray = new String[] {str, str1, str2};

System.out.println("fArray: " + Arrays.toString(fArray));// fArray: [hello world, hello , world]

2.8 String[] to String

StringBuilder sb5 = new StringBuilder();

for(String tmp:fArray) {

sb5.append(tmp);

}

System.out.println("sb5: " + sb5.toString());// sb5: hello worldhello world

2.9 数组 to StringBuilder

//2.9 数组 to StringBuilder

StringBuilder sb6 = new StringBuilder();

for(int i=0;i<fArray.length;i++) {

sb6.append(fArray[i]);

}

System.out.println("sb6: " + sb6);// sb6: hello worldhello world

2.10 StringBuilder to 数组

String[] gArray = new String[] {sb4.toString(), sb6.toString()};

System.out.println("gArray: " + Arrays.toString(gArray));// gArray: [hello world, hello worldhello world]

2.11 ArrayList to StringBuilder

StringBuilder sb7 = new StringBuilder();

for(String tmp:arrList2) {

sb7.append(tmp);

}

System.out.println("sb7: " + sb7);// sb7: hello worldhello world

2.12 StringBuilder to ArrayList

ArrayList<String> arrList3 = new ArrayList<String>();

arrList3.add(sb6.toString());

arrList3.add(sb7.toString());

System.out.println("arrList3: " + arrList3);// arrList3: [hello worldhello world, hello worldhello world]

2.13 String to char[] 

String str3 = "hello world";

char[] ch = str3.toCharArray();

System.out.println("ch: " + Arrays.toString(ch));// ch: [h, e, l, l, o, , w, o, r, l, d]

2.14 char[] to String  

String str4 = String.valueOf(ch);

System.out.println("str4: " + str4);// str4: hello world

 3. 数组常用操作方法

3.1 检查数组中是否含有某个变量

System.out.println(Arrays.asList(gArray).contains("hello"));// false

System.out.println(Arrays.asList(gArray).contains("hello world"));// true

3.2 数组中的元素翻转

Collections.reverse(Arrays.asList(gArray));

System.out.println("gArray: " + Arrays.toString(gArray));// gArray: www.honghgjpt.com [hello worldhello world, hello world]

3.3 数组转Set

Set<String> set = new HashSet<String>(Arrays.asList(gArray));

System.out.println("set: " + set);// set: [hello worldhello world, hello world]

3.4 int数组转成string数组

int[] num = {1, 2, 3, 4, 5, 6, 7, 8, 9};

System.out.println("num: " + Arrays.toString(num));// num: [1, 2, 3, 4, 5, 6, 7, 8, 9]

3.5 数组排序

int[] num1 = {2, 4, 3, 1, 6, 7, 5, 8, 9, 0};

String[] hArray = {"world", "hello", "today", "word"};

Arrays.sort(num1, 4, 9);

System.out.println("originnum1: " + Arrays.toString(num1));// originnum1: [2, 4, 3, 1, 5, 6, 7, 8, 9, 0]

System.out.println("sort1num1: " + Arrays.toString(num1));// sort1num1: [2, 4, 3, 1, 5, 6, 7, 8, 9, 0]

Arrays.sort(num1);

System.out.println("sort2num1: " + Arrays.toString(num1));// sort2num1: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Arrays.sort(hArray);

System.out.println("sort3hArray: " + Arrays.toString(hArray));www.myptvip8.com/ // sort3hArray: [hello, today, word, world]

 3.6 数组复制

String[] iArray = {"a", "d", "c", "k", "y"};

String[] jArray = Arrays.copyOf(iArray, 10);

String[] kArray = Arrays.copyOfRange(iArray, 2, 4);

System.out.println("copy1jArray: " + Arrays.toString(jArray));// copy1jArray: [a, d, c, k, y, null, null, null, null, null]

System.out.println("copy2jArray: " + Arrays.toString(kArray));// copy2jArray: [c, k]

3.7 数组比较

System.out.println(Arrays.equals(iArray, jArray));// false

System.out.println(Arrays.equals(iArray, iArray));// true

3.8 数组去重

String[] lArray = {"a", "d", "y", "c", "a", "k", "y"};

Set<String> set1 = new HashSet<String>(Arrays.asList(lArray));

System.out.println("set1: " + set1);// set1: [a, c, d, y, k]

String[] mArray = new String[set1.size()];

set1.toArray(mArray);

System.out.println("mArray: " + Arrays.toString(mArray));// mArray: [a, c, d, y, k]

3.9查找最小值

Arrays.sort(lArray);

System.out.println("minword: " + lArray[0]);// minword: a

3.10 删除String中的一个字符

StringBuilder sb8 = new StringBuilder(str4);

sb8.deleteCharAt(3);

System.out.println("sb8: " + sb8);www.shengyunyule.cn// sb8: helo world

3.11 删除数组中的一个元素

ArrayList<String> arrList4 = new ArrayList<String>(Arrays.asList(mArray));

arrList4.remove(2);

System.out.println("arrList4: " + Arrays.toString(arrList4.toArray()));// arrList4: [a, c, y, k]

参考链接：

http://www.shengbangyule178.cn t/view/852.html

https://www.078881.cn/ csdn.net/renfufei/article/details/16829457

https://www.suolaieyule.com/ /epeter/p/5664926.html