【弄nèng - 化繁为简】Java字符转大小写

化繁为简，想你所想

1. Java字符转大小写

输入

    public static void main(String[] args) {
        String str = "it-ClouD";
        System.out.println("转换为大写: " + str.toUpperCase());
        System.out.println("转换为大写: " + str.toLowerCase());
    }

输出

转换为大写: IT-CLOUD
转换为大写: it-cloud

2. 源码拓展scan, break scan;

看源码String.java的toUpperCase(Locale locale)方法中有一段有意思的代码，如下:

scan, break scan;

        scan: {
            for (firstLower = 0 ; firstLower < len; ) {
                int c = (int)value[firstLower];
                int srcCount;
                if ((c >= Character.MIN_HIGH_SURROGATE)
                        && (c <= Character.MAX_HIGH_SURROGATE)) {
                    c = codePointAt(firstLower);
                    srcCount = Character.charCount(c);
                } else {
                    srcCount = 1;
                }
                int upperCaseChar = Character.toUpperCaseEx(c);
                if ((upperCaseChar == Character.ERROR)
                        || (c != upperCaseChar)) {
                    break scan;
                }
                firstLower += srcCount;
            }
            return this;
        }                   

该段代码的作用是跳出多重循环嵌套

使用示例

输入

    public static void main(String[] args) {
        System.out.println("====开始====");
        ok: {
            for (int i = 0; i < 5; i++ ) {
                System.out.println("START-" + i + "");
                for (int j = 0; j < 5; j++) {
                    System.out.println(j);
                    if (j == 2) {
                        break ok;
                    }
                }
                System.out.println("END-" + i + "");
            }
        }
        System.out.println("====结束====");
        
    }

输出

====开始====
START-0
0
1
2
====结束====

当把break ok;改成break;时输出如下: 显而易见只跳出来内循环

====开始====
START-0
0
1
2
END-0
START-1
0
1
2
END-1
START-2
0
1
2
END-2
START-3
0
1
2
END-3
START-4
0
1
2
END-4
====结束====