数组、字符串、字符常用操作

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int[][] test = {{1,2,3}, {4,5,6}, {7,8,9}};
for (int i = 0; i < test.length; i++) {
System.out.println(Arrays.toString(test[i]));
}

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public static String toString(int[] a) {
if (a == null)
return "null";
int iMax = a.length - 1;
if (iMax == -1)
return "[]";
// 往StringBuilder中追加元素
StringBuilder b = new StringBuilder();
b.append('[');
for (int i = 0; ; i++) {
b.append(a[i]);
if (i == iMax)
return b.append(']').toString();
b.append(", ");
}
}

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int[] nums = {4,3,5,6,7};
Arrays.sort(nums);

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int[] arr= {4,3,5,6,7};
int[] temp = Arrays.copyOf(arr, arr.length);

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public static int[] copyOf(int[] original, int newLength) {
int[] copy = new int[newLength];
// 调用另一个数组赋值函数
System.arraycopy(original, 0, copy, 0,
Math.min(original.length, newLength));
return copy;
}

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int[] heights = {1,3,5,3,1};
int[] test = new int[heights.length];
System.arraycopy(heights, 0, test, 0, heights.length);

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Arrays.equals(chars, chars1);

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String str = "a-bC-dEf-ghIj";
char[] cs = Str.toCharArray();

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public char[] toCharArray() {
// Cannot use Arrays.copyOf because of class initialization order issues
char result[] = new char[value.length];
// 使用的是System.arraycopy()数组复制方法
System.arraycopy(value, 0, result, 0, value.length);
return result;
}

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//第一个substring：从第n个字符开始截取到最后一个字符
//第二个substring：从0开始截取到第n个字符
return s.substring(n) + s.substring(0, n);

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// 获取第i个字符和第j个字符
str.charAt(i) != str.charAt(j)

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// 字符串"abc"中是否存在子串"ab"
"abc".contains("ab")

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// 使用空格将字符串分割成若干份子字符串
String[] s1 = str.split(" ")

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// 将字符串str中的"."串置换为"[.]"
str.replace(".", "[.]");

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String str = "
";
if (str.trim().isEmpty()) {
System.out.println("是由空格组成");
}

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String str = "ROLE_lwz";
if (str.startsWith("ROLE_")) {
System.out.println("字符串是以ROLE_开头");
}

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for (char c : str.toCharArray()) {
// 判断字符是否是字母
if (Character.isLetter(c)) {
}
}

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// 将字符串中的每个字符取出后减去字符‘0’
num1.charAt(i) - '0'

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// 判断字符是否为数字或者字母
Character.isLetterOrDigit(ch)

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StringBuffer stringBuffer = new StringBuffer(str);

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stringBuffer.toString();

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// 往StringBuilder中追加元素
StringBuilder b = new StringBuilder();
b.append('[');

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b.reverse();