Java - String을 double로 변환

String str = "123.456";

double num = Double.parseDouble(str);

System.out.println(num);

123.456

String str = "123.456";

Double num = Double.valueOf(str);

System.out.println(num);

123.456

String str = "a123.456";

Double num = Double.valueOf(str);

Exception in thread "main" java.lang.NumberFormatException: For input string: "a123.456"
	at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2054)
	at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
	at java.base/java.lang.Double.parseDouble(Double.java:549)
	at java.base/java.lang.Double.valueOf(Double.java:512)
	at ConvertNumbersToString.main(ConvertNumbersToString.java:57)

String str = "a123.456";

Double num;
try {
    num = Double.valueOf(str);
} catch (NumberFormatException e){
    num = 0.0;
}