Three methods for converting java objects to String type

1. Use Object.toString()
The toString method is a public method of the java.lang.Object object. Any object in Java will inherit the Object object, so generally any object can call the toString method. This is when using this method, often derived classes will override the toString() method in Object.
But when using this method, please note that the Object must not be a null value, otherwise a NullPointerException will be thrown.

2. Use (String)Object
This method is a standard type conversion method that can convert Object to String. However, when using this method, please note that the type to be converted must be convertible to String, otherwise a CalssCastException error will occur.

Object o = new Integer(100);
String string = (String)o;

This program code will cause java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String. Because the Integer type is cast to the String type, it cannot be passed.

3. String.valueOf(Object)
We need to worry about the null problem when using the Object.toString() method above. But there is no need to worry about null values ​​using this method. Because when using String.valueOf(Object), it will determine whether the Object is a null value, and if so, return null. The following is the source code of String.valueOf(Object):

public static String valueOf(Object obj) {
     return (obj == null) ? "null" : obj.toString();
}

From the above we can see two points: First, there is no need to worry about the null problem. Second, it is based on the toString() method.
But be sure to note: when object is null, the value of String.valueOf(object) is the string object: "null", not null! ! !

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