java regular expression to validate whether the input is legal

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1 determines whether the string can be converted to a positive integer, (+, -, or zero)
    public static Boolean isNumber (String STR) {
        String REG = "^ [1-9] [0-9] {0,} $ ";
        return str.matches (REG);
    }

2. determining whether the string can be converted to integer or floating point

    public static boolean isNumber(String str){
        String reg = "^[0-9]+(.[0-9]+)?$"; 
        return str.matches(reg);
    }

3. determining whether the character string can be converted for all integers

public static boolean isNumber(String str){
    String reg = "^\-{0,1}[0-9]{1,}$"; 
    return str.matches(reg);
 }