[Java知识库]当对象为null时，如何toString()

package aa;

import org.apache.commons.lang3.StringUtils;

import java.util.Objects;

public class AADemo_4 {
    public static void main(String[] args) {
        User1 user1 = new User1("xiaowang",17);
        User1 user11 = null;
        System.out.println(user1.toString());
        try{
            System.out.println(user11.toString());
        }catch (NullPointerException e){
            e.printStackTrace();
        }
        System.out.println(String.valueOf(user1));
        System.out.println(String.valueOf(user11) == "null");
        System.out.println(StringUtils.isBlank(String.valueOf(user11)));
        System.out.println(StringUtils.isEmpty(String.valueOf(user11)));
        System.out.println(StringUtils.isBlank("    "));
        System.out.println(StringUtils.isEmpty("    "));
        System.out.println(Objects.toString(user11, null));
        /**
         * User1{name='xiaowang', age=17}
         * User1{name='xiaowang', age=17}
         * true
         * false
         * false
         * true
         * false
         * null
         * java.lang.NullPointerException
         * 	at aa.AADemo_4.main(AADemo_4.java:13)
         */
    }
    static class User1{
        String name;
        Integer age;

        public User1(String name, Integer age) {
            this.name = name;
            this.age = age;
        }

        @Override
        public String toString() {
            return "User1{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
}

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