java == 引发的线上异常详解

class Scratch {
    public static void main(String[] args) {
        JSONArray arrays = JSONUtil.parseArray("[{'type':1},{},{'type':2},{'type':2}" +
                ",{'name':'zhangsan'},{'type':1},{'type':1},{'type':1}]");
        List<User> users = JSONUtil.toList(arrays, User.class);
        Set<User> set = users.stream().filter(u -> u.getType() == 1).collect(Collectors.toSet());
        System.out.println(set);
    }
    @Data
    static class User {
        private String name;
        private Integer type;
    }
}

Exception in thread "main" java.lang.NullPointerException
	at Scratch.lambda$main$0(scratch.java:14)
	at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174)
	at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
	at Scratch.main(scratch.java:14)

u -> u.getType() == 1

1 == 1 // true
1 == 2 // false
1.33 == 1.33 // true

null == Integer.valueOf(1) // false
new Integer(1) == Integer.valueOf(1) // false

Integer val1 = new Integer(13);
Integer val2 = new Integer(13);
val1 == val2; // false

null == 1 // NullPointerException

1 == Integer.valueOf(1); // true
1 == new Integer(1); // true

Objects.equals(null,1); // false

public static boolean equals(Object a, Object b) {
    return (a == b) || (a != null && a.equals(b));
}